DESCRIPTION Title of Invention AIR CONDITIONER Technical Field [0001] The present invention relates to an air conditioner in which a cross flow fan is mounted as blower means. Background Art [0002] A prior-art air conditioner, in which a cross flow fan is mounted, having small holes (dimples) in the surface of a casing, has been disclosed (See Patent Document 1, for example). In this air conditioner in which the cross flow fan is mounted, small holes (dimples) are disposed at equal intervals and in a lattice in a planar side wall in a direction perpendicular to a rotary shaft of the fan in a blow-out grill. By forming the dimples in plural, reduction of separation in a high air-speed region from a fan blow-out portion to a ventilation flue is attempted. [0003] Also, an air conditioner in which swirl generating means is formed on the surface of a casing has been disclosed (See Patent Document 2, for example). In this air conditioner in which a cross flow fan is mounted, the swirl generating means is disposed on the downstream side, when seen from the fan located on the casing surface, and generates a longitudinal swirl in the air flowing out via the fan. By means of this swirl generating means, the longitudinal swirl is generated in a swirl generation portion, and by agitating an upper layer and a lower layer in the air, separation of the flow from the casing surface is prevented. Citation List Patent Literature [0004] Patent Literature 1: Japanese Unexamined Patent Application Publication No. 8-121396 (pages 4 and 5, Fig. 6) Patent Literature 2: Japanese Unexamined Patent Application Publication No. 2002-250534 (pages 2 and 3, Fig. 2) Summary of Invention Technical Problem [0005] In the air conditioner described in Patent Literature 1, in which the cross flow fan is mounted, since the dimples (small holes) formed in plural in a lattice in the casing surface are semispherical holes, when a fan blow-out flow passes through the surfaces of dimples, the direction on the dimple downstream side is not set down and might become unstable, which is a problem. [0006] Also, in the cross flow fan described in Patent Literature 2, since the longitudinal swirl is generated in the swirl generation portion projecting from the casing surface, an upstream-side surface of the swirl generation portion is directed to a stabilizer so as to block the fan blow-out flow. Thus, the flow is disturbed and becomes ventilation resistance, the torque is increased in rotation of the fan, and as a result, an input of a driving fan motor might be deteriorated, which is also a problem. [0007] The present invention was made in order to solve the above problems and an object thereof is to obtain an air conditioner having a cross flow fan which enable to prevent separation from the casing in an air path that air blowing out of the fan blows into a room through a blow-out port, to reduce noise, and to prevent an increase in an input of a driving fan motor. Also, prevention of dew splashing generated by cooling the indoor air by the low-temperature air since counterflow of the indoor air is generated by a reduced speed of the blown-out air at both end portions in a direction of a rotary shaft of the fan is also an object. Solution to Problem [0008] An air conditioner according to the present invention is provided with an inlet through which indoor air is sucked, a heat exchanger that exchanges heat with the sucked indoor air, a blow-out port through which the heat-exchanged indoor air is blown out into a room, a blower having an impeller, disposed on the downstream side of the heat exchanger between the inlet and the blow-out port, rotated and driven by a motor and feeding the indoor air from the inlet to the blow-out port, with a longitudinal direction of an air conditioner main body as its rotary shaft direction, a stabilizer that separates a suction-side channel on the upstream side of the impeller and a blow-out-side channel on the downstream side from each other and forms a front face side of the blow-out-side channel from the impeller to the blow-out port, a spiral guide wall that forms a rear face side of the blow-out-side channel from the impeller to the blow-out port, and a stepped portion disposed at least in a part of the guide wall and having a plurality of steps, each indented substantially in a triangular shape in a section perpendicular to the rotary shaft of the impeller and extending in the rotary shaft direction, and forming steps in a direction in which the blower feeds the air. Advantageous Effects of Invention [0009] According to the present invention, an air conditioner can be obtained in which separation from a casing is prevented while a high-speed air flow blown out of the fan flows to the blow-out port, noise is reduced, and energy can be saved. Also, an air conditioner can be obtained in which, at the both ends in the rotary shaft direction of the fan, the air flow on the center side in the vicinity thereof is drawn and counterflow from inside of the room can be prevented. Brief Description of Drawings [0010] [Fig. 1] Fig. 1 relates to Embodiment 1 of the present invention and is an external perspective view illustrating an air conditioner in which a cross flow fan is mounted. [Fig. 2] Fig. 2 is longitudinal sectional view taken along the Q-Q line in Fig. 1. [Fig. 3] Fig. 3 is an outline configuration diagram illustrating an impeller of a cross flow fan mounted in the air conditioner according to Embodiment 1. [Fig. 4] Fig. 4 is a perspective view illustrating a housing forming a part of a main body outer shell integrated with a guide wall of the air conditioner according to Embodiment 1 and the impeller of the cross flow fan. [Fig. 5] Fig. 5 relates to the air conditioner according to Embodiment 1 and is a perspective view illustrating a housing rear face portion when the impeller of the cross flow fan is removed. [Fig. 6] Fig. 6 relates to the air conditioner according to Embodiment 1 and is an explanatory diagram illustrating a section of a part in the vicinity of the guide wall in an enlarged manner. [Fig. 7] Fig. 7 relates to the air conditioner according to Embodiment 1 and is an explanatory diagram illustrating a section of a part of a stepped portion in an enlarged manner. [Fig. 8] Fig. 8 relates to the air conditioner according to Embodiment 1 and is an explanatory diagram illustrating an action of the stepped portion. [Fig. 9] Fig. 9 relates to the air conditioner according to Embodiment 1 and is a perspective view in the air conditioner main body illustrating a configuration in which a suction grill is divided in the main body longitudinal direction on an upper part. [Fig. 10] Figs. 10 relates to the air conditioner according to Embodiment 1 and Fig. 10(a) is an explanatory diagram illustrating distribution of a blow-out air velocity V from the impeller, in which the horizontal direction indicates the rotary shaft direction of the impeller and the vertical direction indicates the air velocity A. Fig. 10(b) is a front view illustrating the guide wall and the housing rear face portion formed integrally with the guide wall, and illustrating without the impeller of the cross flow fan, but the position of the impeller is indicated by a dotted line. [Fig. 11] Fig. 11 relates to the air conditioner according to Embodiment 1 and is a perspective view illustrating the guide wall and the housing rear face portion formed integrally with the guide wall. [Fig. 12] Fig. 12 relates to the air conditioner according to Embodiment 1 and is an explanatory diagram, in which the horizontal direction indicates the direction of the impeller rotary shaft and the vertical direction indicates an air velocity V. [Fig. 13] Fig. 13 relates to an air conditioner according to Embodiment 2 of the present invention and is a front view illustrating a guide wall and a housing rear face portion formed integrally with the guide wall. [Fig. 14] Fig. 14 relates to the air conditioner according to Embodiment 2 and is a perspective view illustrating the guide wall and the housing rear face portion formed integrally with the guide wall. [Fig. 15] Fig. 15 relates to the air conditioner according to Embodiment 2 and is an explanatory illustrating a blow-out flow in the vicinity of the guide wall close to an impeller unit body at both ends in the rotary shaft direction on a section perpendicular to a rotary shaft O of a cross flow fan. [Fig. 16] Fig. 16 relates to the air conditioner according to Embodiment 2 and is a perspective view illustrating the guide wall and the housing rear face portion formed integrally therewith when the impeller of the cross flow fan is removed. [Fig. 17] Fig. 17 relates to the air conditioner according to Embodiment 2 and is a perspective view illustrating the guide wall and the housing rear face portion formed integrally therewith when the impeller of the cross flow fan is removed. [Fig. 18] Fig. 18 relates to the air conditioner according to Embodiment 2 and is a perspective view illustrating the housing rear face portion when the impeller of the cross flow fan is removed. [Fig. 19] Fig. 19 relates to the air conditioner according to Embodiment 2 and is a perspective view illustrating the guide wall and the housing rear face portion formed integrally therewith when the impeller of the cross flow fan is removed. [Fig. 20] Fig. 20 relates to an air conditioner according to Embodiment 3 and is an exploded perspective view illustrating a guide wall and a housing rear face portion formed integrally therewith when the impeller of the cross flow fan is removed. Description of Embodiments [0011] Embodiment 1 Embodiment 1 of the present invention will be described below by referring to the attached drawings. Fig. 1 is an external perspective view of this embodiment, illustrating an air conditioner in which a cross flow fan is mounted as a blower, Fig. 2 is a longitudinal sectional view taken along the Q-Q line in Fig. 1, Fig. 3 is an outline configuration diagram illustrating an impeller of the cross flow fan mounted in the air conditioner according to this embodiment, Fig. 4 is a perspective view illustrating a housing that forms a part of a main body outer shell integrated with a guide wall and the impeller of the cross flow fan of the air conditioner according to this embodiment, Fig. 5 is a perspective view illustrating a housing rear face portion 1c when the impeller 8a of the cross flow fan is removed according to this embodiment, Fig. 6 is an explanatory diagram illustrating a section of a part in the vicinity of the guide wall in an enlarged manner, and Fig. 7 is an explanatory diagram illustrating a section of a part of a stepped portion 14 in an enlarged manner. An air flow is indicated by non-filled arrows in Fig. 1 and by dotted arrows in Figs. 2 and 6. Also, bold arrows RO in Figs. 2 and 4 indicate a rotation direction of the impeller 8a of the cross flow fan 8. Also, reference character 0 designates a rotary shaft of the impeller 8a and indicates the rotation center in the sectional view. [0012] As illustrated in Figs. 1 and 2, an air conditioner main body 1 is installed on a wall 11a of a room 11 to be air conditioned. The air conditioner main body 1 is composed of a front panel 1a disposed on the main body front, a housing front face portion 1b, and the housing rear face portion 1c. In an air conditioner main body upper part 1d extending across the housing front face portion 1b and the housing rear face portion 1c, an inlet 2 for indoor air is formed, and moreover, an electric dust collector 6 that electrostatically collects dust, a mesh filter 5 that removes dust, and a heat exchanger 7 are disposed on the upstream side of the impeller 8a of the cross flow fan 8, which is a blower. [0013] As illustrated in Fig. 2, a stabilizer 9, which has a shape extending to the vicinity of the impeller 8a, separates a suction-side channel E1 on the upstream side of the impeller 8a and a blow-out-side channel E2 on the downstream side from each other, forms a front face side of the blow-out-side channel E2 from the impeller 8a to a blow-out port 3 and also has such a shape as to be able to temporarily collect droplets dropping from the heat exchanger 7. Also, the rear face side of the blow-out-side channel E2 from the impeller 8a to the blow-out port 3 is constructed by a spiral guide wall 10, and the guide wall 10 is formed integrally with the housing rear face portion 1c. The term "guide wall 10" refers to a portion from a guide-wall start point 10a, which is the closest portion to the impeller 8a on the upstream side, to a guide-wall end point 10b, which is the closest point to the stabilizer 9 on the downstream side. Straight lines connecting the rotation center O to the guide-wall start point 10a and the guide-wall end point 10b, respectively, form a spiral angle 9c, which is a predetermined angle. Also, straight lines connecting each position of the guide wall 10 to the rotary shaft center O are formed in the spiral shape from the guide-wall start point 10a to the guide-wall end point 10b such that the lines become longer substantially gradually. In a part of the guide wall 10, a plurality of recess portions are consecutively provided in a stepped shape from the impeller 8a to the blow-out port 3 so as to form a stepped portion 14. Moreover, at the blow-out port 3, a vertical air-direction vane 4a and a horizontal air-direction vane 4b are mounted rotatably. [0014] In Fig. 3 illustrating the impeller 8a of the cross flow fan 8, a single blade 8c is shown on the upper side of the rotary shaft O, and a view seen from the front is shown on the lower side of the rotary shaft O. As illustrated in Fig. 3, the impeller 8a of the cross flow fan 8 is molded from a thermoplastic resin such as AS, for example. One end portion of the blade 8c extending in a rotary shaft direction L is fastened to an outer peripheral portion of the disk-shaped ring 8b, and a plurality of the blades 8c are disposed along the outer peripheral portion of the ring 8b so as to obtain an impeller unit body 8d. The other end portion of the blade 8c of the one impeller unit body 8d and the back face (the surface on which the blade 8c is not fastened) of the ring 8b of the adjacent impeller unit body 8d are adhered together. After a plurality of impeller unit bodies 8d have been adhered together, the ring 8b that becomes an end portion of the impeller 8a is welded so as to form the impeller 8a. Moreover, on one end of the impeller 8a, a fan shaft 8f forming the rotary shaft O is fastened using a screw or the like, for example. On the other end of the impeller 8a, a fan boss 8e formed integrally with the ring 8b, and a motor shaft 12a of a motor 12, for example, are fixed by a screw or the like. The both end portions are supported by the fan shaft 8f and the fan boss 8e. With rotation of the motor 12, the impeller is rotated in the rotation direction RO as shown in Fig. 2 around the rotary shaft O as the rotation center, and the indoor air is sucked through the inlet 2 and is blown out into the room through the blow-out port 3. The impeller 8a is contained in the air conditioner main body 1 so that the rotary shaft direction L of the impeller 8a matches the longitudinal direction of the air conditioner main body 1. [0015] In Figs. 4 and 5, on the downstream side of the guide wall 10, surging blocks 15, for example, are formed as channel reducing members on both end portion sides of the impeller 8a. By means of these surging blocks 15, the width of the blow-out side channel E2 is decreased. By decreasing the width of the flow, lowering of the speed of air flow blown out of the impeller 8a is prevented in the vicinity of the both end portions of the impeller 8a, and counterflow of the air in the room is prevented. Also, the stepped portion 14 is disposed in a part of the guide wall 10. The stepped portion 14 disposed on the guide wall 10 is, as shown in Fig. 5, formed in a part of the impeller 8a in the rotary shaft direction L or at the center part here. In the flow along the guide wall 10, a blown-out flow at the center part in the rotary shaft direction L is a relatively high-speed flow Ff. On the other hand, the blown-out flows at the both end portions of the rotary shaft direction L are blown-out flows Fs, which are slower than the flow at the center part. [0016] Also, as shown in Fig. 6, the stepped portion 14 has a plurality of steps, each extending in the rotary shaft direction L and indented in a substantially triangular shape in a section perpendicular to the rotary shaft O of the impeller 8a or five steps 14A, 14B, 14C, 14D, and 14E here disposed in parallel in a stepped shape. A step start portion 14a of the step portion 14A located farthest upstream to a step end portion 14d of the step portion 14E located farthest downstream are formed inside from the guide-wall start point 10a to the guide-wall end point 10b. Also, lengths C1, C2, and C3 of line segments 0-14a, 0-14b, and 0-14d connecting the rotation center O of the impeller 8a of the cross flow fan to each of the step start point 14a, a step deepest point 14b, and the step end portion 14d have a relationship of C1 < C2 < C3. Also, in each of the steps 14A, 14B, 14C, 14D, and 14E, the step deepest portion 14b is located close to the step start portion 14a side between the step start portion 14a and the step end portion 14d. That is, a distance h connecting the step start portion 14a to the step deepest portion 14b and a length S connecting the step deepest point 14b to the step end portion 14d are in a relationship of h < S. A plane connecting the step deepest point 14b and the step end portion 14d is a step slope portion 14c, which is a flat inclined plane facing the impeller 8a. [0017] As shown in Figs. 6 and 7, since the stepped portion 14 disposed on the guide wall 10 satisfies the relationship of C1 < C2 < C3, the step portion is formed in a direction gradually expanding toward downstream of the blow-out-side channel E2 from the rotation center O. For example, the cross flow fan 8 with the impeller 8a of the diameter of 53 mm is used, and in the step 14A farthest upstream side, C1 = 76 mm, C2 = 78 mm, and C3 = 79 mm are set. In the step 14B connected to the step 14A, C1 = 79 mm is set, and the steps 14C to 14E are formed consecutively. Also, in each of the plurality of steps 14A, 14B, 14C, 14D, and 14E, the distance h connecting the step start portion 14a to the step deepest portion 14b and the distance S connecting the step deepest point 14b to the step end portion 14d are set in a substantially similar way and they are set approximately at h = 2 mm and S = 15 mm, for example, and formed with h/S of approximately 0.1 to 0.3. However, since they are formed such that the spiral surface of the guide wall 10 of a configuration in which the stepped portion 14 is not disposed or a spiral virtual surface IM of the guide wall 10 is formed here by connecting the step start portion to the step end portion of each of the steps 14Ato 14E, the distances h and S of each step in the stepped portion 14 do not necessarily have to be the same. [0018] Also, a stepped-portion forming angle θs, which is an angle from the step start portion 14a of the step portion 14A to the step end portion 14d of the step portion 14E around the rotation center O is an angle smaller than a spiral angle 0c from the guide-wall start point 10a to the guide-wall end point 10b. Supposing that the stepped-portion forming angle 9s formed by a straight line connecting the rotation center O to the step deepest point 14b of the step portion 14A and a straight line connecting the rotation center O to the step end portion 14d of the step portion 14E farthest downstream side is a predetermined angle or approximately 60°, for example, and the guide wall spiral angle 6c is approximately 140°, for example, the angle 6s is formed so as to be approximately 1/2 the angle 6c. [0019] The stepped portion 14 will be described below in more detail on the basis of Fig. 7. One step constituting the stepped portion 14 has a sectional substantially triangular shape indented from the spiral virtual surface IM of the guide wall 10. That is, the step deepest portion 14b is formed at a position lowered from the step start portion 14a located on the start point 10a side of the guide wall 10 toward the rear face side (in a direction to the right in Fig. 7) of the guide wall 10 by approximately 90 degrees (01). Moreover, the step slope 14c, which is a face extending along the virtual surface IM in the direction of approximately 80 degrees (02), is formed from the step deepest portion 14b toward the virtual surface IM of the guide wall 10. A portion where the step slope 14c crosses the virtual surface IM is the step end portion 14d. Here, an angle (63) formed by the step slope 14c and the virtual surface IM at the step end portion 14d is approximately 10 degrees or less. For example, the step start portion 14a, the step deepest portion 14b, and the step end portion 14d form one step 14B indented to a substantially triangular shape. [0020] In the air conditioner main body 1 configured as above, if the motor 12 which rotates and drives the impeller 8a is electrified by a power-supply substrate, the impeller 8a of the cross flow fan 8 is rotated in the RO direction. Then, the air in the room 11 is sucked through the inlet 2 disposed in the air conditioner main body upper part 1d, and after dust has been removed by the electric dust collector 6 and the filter 5, the air is heat-exchanged by the heat exchanger 7. That is, the air is heated and used for heating or is cooled and used either for cooling and dehumidification, flows through the suction-side channel E1 and is sucked into the impeller 8a of the cross flow fan 8. After that, the flow blown out of the impeller 8a is guided to the guide wall 10 and the stabilizer 9 and passes through the blow-out-side region E2 toward the blow-out port 3. Then, the flow is blown out into the room 11 for air conditioning. At this time, the direction of the blown-out air is controlled vertically and horizontally by the vertical air-direction vane 4a and the horizontal air-direction vane 4b so as to allow the air to flow through the entire room 11 and to suppress uneven temperature. [0021] At this time, at the center part in the rotary shaft direction L of the blow-out region E2, the relatively high-speed flow Ff blown out of the impeller 8a and flowing along the guide wall surface collides with the guide wall 10 and is fed to the blow-out port 3. Also, a blow-out air-velocity difference is generated between the adjacent impeller unit bodies 8d in the rotary shaft direction L of the impeller 8a, and a disturbance is caused by shearing friction between the blow-out flows particularly in the vicinity of the ring 8b. The guide wall 10 in the prior-art air conditioner has a merely curved spiral shape. Thus, the collision of the blow-out air and the collision of the disturbance flows on the surface of the guide wall 10 cause pressure fluctuations and noise. Particularly, at the center part of the rotary shaft direction L, the blow-out flow is the high-speed flow Ff, and since the flow Ff collides with the guide wall 10 at a high speed, the noise gets louder. [0022] Here, in this embodiment, the stepped portion 14 shown in Figs. 5 to 7 is disposed at the center part, for example, of the guide wall 10. Through the center part, the high-speed flow Ff flows, and an action of the stepped portion 14 with respect to this high-speed flow Ff will be described using an explanatory diagram in Fig. 8. As shown in Fig. 8, a part of the high-speed flow Ff flowing along the stepped portion 14 changes its direction at the step start portion 14a of the step 14A farthest upstream side to the step deepest portion 14b and drops into the step 14A and generates a swirl G1. Thus, in the step deepest portion 14b, a negative pressure is generated by the swirl G1. In this state, the high-speed blown-out flow Ff further blown out of the impeller 8a and flowing in the vicinity of the surface of the guide wall 10 is drawn by the negative pressure from the step start portion 14a as shown by a flow X and adheres again to a part on the downstream side of the step slope 14c. Then, the flow goes toward the step portion 14B provided consecutively to the step portion 14A. A similar phenomenon also occurs at the step start portion 14a of the step portion 14B, and the flow adheres again to the step slope 14c in the middle of the step portion 14B. By means of the stepped portion 14 in which a plurality of steps are formed, the phenomenon that the flow is separated from the surface of the guide wall 10 at the step start portion 14a and adheres again in the middle of the step slope 14c is repeated so that the flow flows as the flow X. Thus, as compared with the blown-out flow Ff in the case without the stepped portion 14, the surface area of the guide wall 10 in contact with the high-speed flow is reduced in the blown-out flow X. As a result, a sound source is decreased. Also, since the negative pressure is generated by the swirl G1, separation on the surface of the guide wall 10 is suppressed. [0023] Also, a distribution is generated in the flow velocity of the blown-out flow with respect to the rotary shaft direction L. In this embodiment, the stepped portion 14 is disposed so as to extend in the rotary shaft direction L. Thus, the size of the swirl G1 changes along with the rotary shaft direction L, and pressure fluctuations are alleviated in the rotary shaft direction L. Moreover, since the steps are provided consecutively in plural like the steps 14A, 14B, 14C, 14D, and 14E, the pressure fluctuations of the blown-out flow Ff are gradually diffused. As a result, noise can be further reduced. [0024] Also, by preventing separation of the flow from the surface of the guide wall 10, reduction of an air amount with respect to inputted power can be prevented, which leads to energy saving. Moreover, due to the relationship of C1 < C2 < C3, the step end portion 14d does not protrude toward the air path side of the blow-out-side channel E2 from the virtual surface IM of the guide wall 10 but gradually expands in a shape along the spiral virtual surface IM of the guide wall 10, and thus, the step end portion 14d does not disturb the flow in the vicinity of the guide wall 10 having flowed from upstream. Thus, the ventilation resistance is reduced, the motor power can be reduced, and power consumption can be also reduced. [0025] As a result, by providing the stepped portion 14, a lower noise and higher efficiency can be realized for the cross flow fan, and an air conditioner that is silent and can save energy can be obtained by mounting this cross flow fan. [0026] The step start portion 14a and the step end portion 14d are located on the spiral virtual surface IM of the guide wall 10, and the step deepest portion 14b is located at a portion indented toward the rear face side of the guide wall 10 from the virtual surface IM. Here, since the guide wall 10 is in the spiral shape, C1 < C3 is satisfied all the time. Satisfaction of C1 < C2 indicates that the step deepest portion 14b is located at the portion indented toward the rear face side of the guide wall 10 from the step start portion 14a. Also, the relationship of C2 < C3 indicates that the position of the step deepest portion 14b is not largely indented from the virtual surface IM. Supposing that a circle passing through the step end portion 14d of one step is drawn around the rotation center of the impeller 8a on the section shown in Fig. 8, for example, it is only necessary that the step be formed so that the step deepest portion 14d is located inside the circle. Then, it is only necessary that the steps 14A, 14B, 14C, 14D and 14E be formed with a minimum indent width (= C2 - C1) sufficient to generate the swirl G1 and to create a negative pressure in this portion. If a step with a large indent width is provided, a large swirl is generated in this portion, and the large swirl rather disturbs the blown-out flow flowing along the guide wall 10. [0027] Also, in the configuration with h 03. Thus, the swirl G1 can easily occur at a portion close to the step start portion 14a. Moreover, the length of the slope 14c is set longer so as to have a shape which makes re-adhesion easy. Also, h/S is preferably set to 0.1 to 0.3. If h/S is smaller than 0.1, the indent is too small and the swirl becomes small, and the effect of re-adhesion is also small. On the other hand, if h/S is larger than 0.3, the indent is too large and the swirl becomes large, which rather disturbs the flow. [0028] Also, examples of 01, 02, and 03 are shown, but the examples are not limiting. The shape is preferably such that the swirl G1 can easily occur from the flow in the vicinity of the guide wall 10. In that meaning, 01 and 02 are preferably approximately 90° so that the swirl G1 can easily occur from that shape. Particularly, if 02 is 90° or less, the swirl G1 occurs in the vicinity of the step deepest portion 14b, and the flow drawn by the negative pressure can be made to smoothly adhere to the slope 14c again, which is preferable. The angle 03 is set small so that the flow of the step slope 14c can flow smoothly to the step start portion 14a of the subsequent step. [0029] During manufacture, if the entire guide wall 10 is to be manufactured integrally using a die, the shape needs to be such that separation from the die is possible. For example, when a straight line passing through the step start portion 14a of each step and indicating a die separation direction is drawn on the section perpendicular to the rotary shaft direction L, if the step deepest portion 14b is above this straight line, that is, if the portion has a shape located at the portion bitten into the rear face side of the guide wall 10, the separation becomes impossible. Thus, the step deepest portion 14b is preferably located below the straight line passing through the step start portion 14a and indicating the die separation direction. However, if another method of manufacture is used, the above does not necessarily apply. [0030] Also, in this embodiment, the stepped portion 14 is adapted to have five steps, but it is not limited to five, and it is only necessary that two or more steps are provided in parallel. Also, in Fig. 8, for example, the stepped portion 14 is configured such that the adjacent step end portion 14d of the step 14A on the upstream side and the step start portion 14a of the step 14B consecutively connected on the downstream side are consecutively connected substantially at the same positions. The configuration is not limited thereto, but a plurality of steps may be provided with some separation between the step end portion 14d of the step 14A on the upstream side and the step start portion 14a of the step 14B on the downstream side, for example. That is, the similar effect can be obtained as long as the plurality of steps are provided with a predetermined interval and in the stepped shape at least continuously. [0031] Also, the stepped portion 14 may be located anywhere as long as it is between the guide wall start point 10a and the guide wall end point 10b. However, on the side immediately downstream of the guide wall start point 10a, a swirl and the like can be easily generated depending on the shape of the guide wall start point 10a, and the flow can become unstable. In order to obtain an effective advantage from the stepped portion 14, the stepped portion 14 is preferably provided at a portion such that a flow along the guide wall 10 can be obtained to some degree. As shown in Fig. 2, by providing the stepped portion 14 in the vicinity of the flow substantially along the guide wall 10, the action to suppress separation of the flow along the guide wall 10 can be effectively exerted. [0032] Fig. 9 is a perspective view according to this embodiment and illustrates a configuration in which the inlet 2 is divided in the main body longitudinal direction in the air conditioner main body upper part 1d. As shown in Fig. 9, the inlet 2 is divided by a dividing portion 2C in the vicinity of the center in the rotary shaft direction into a first inlet 2A and a second inlet 2B. When the electric dust collector 2 and an additional filter and the like are asymmetrically disposed on the upstream side of the heat exchanger 7 and suction ventilation resistance becomes different between right and left in the configuration, the dividing portion 2C might be disposed in the vicinity of the center. [0033] In this configuration example, as shown in Figs. 6 to 8, by forming the stepped portion 14 extending to the impeller rotary shaft direction L on the guide wall 10, a lower noise and higher efficiency of the cross flow fan 8 can be realized, and an air conditioner that is silent and can save energy can be obtained. If the inlet 2 is divided into two parts in the rotary shaft direction L of the impeller 8a and is composed by the first inlet 2A and the second inlet 2B, the dividing portion 2C that divides the inlet 2 into two parts works as resistance. Thus, suction and blow-out of the impeller 8a become difficult on the downstream side of the dividing portion 2C. Thus, at a position corresponding to the downstream of the dividing portion 2C, a blow-out air velocity might be slower than that in the other regions. Fig. 10(a) illustrates a distribution of a blow-out air velocity V from the impeller 8a. The horizontal direction indicates the impeller rotary shaft direction L, while the vertical direction indicates the air velocity V. As illustrated in the figure, the air velocity V is lowered in the downstream portion of the dividing portion 2C. [0034] Fig. 10(b) is a front view illustrating the guide wall 10 and the housing rear face portion 1c configured integrally therewith without the impeller 8a of the cross flow fan, but the position of the impeller 8a is shown by a dotted line. In Figs. 10(a) and 10(b), the position of the rotary shaft direction L is substantially matched. Also, Fig. 11 is a perspective view illustrating the guide wall 10 and the housing rear face portion 1c configured integrally therewith. In this configuration example, a stepped portion 16 is divided into right and left two parts, that is, a first stepped portion 16A and a second stepped portion 16B corresponding to the first and second inlets 2A and 2B. That is, the stepped portion 16 is not formed in a center part B corresponding to the dividing portion 2C in the vicinity of the center in the rotary shaft direction L. Detailed sectional shapes of the first and second stepped portions 16A and 16B are similar to the stepped portion 14 in Figs. 2 and 6 to 8. [0035] The first and second stepped portions 16A and 16B are formed in portions where the blow-out air velocity of the impeller 8a is relatively high or portions where the blow-out air velocity is Vs or more, for example, which is the guide wall 10. That is, the blow-out air velocity becomes high at positions corresponding to the downstreams of the first and second inlets 2A and 2B, and the flow in the vicinity of the surface of the guide wall shown in Fig. 6 also collides with the guide wall 10 at a high speed. The larger the surface area of the guide wall 10 with which the high-speed flow is in contact, the larger the noise becomes, and a swirl is generated in the vicinities of the step deepest portions of the stepped portions 16A and 16B so that negative pressures are generated in the vicinities. Then, while separation of the high-speed flow flowing through the surface of the guide wall 10 is suppressed, the surface area of the guide wall 10 with which the high-speed flow is in contact is reduced. As a result, the noise can be reduced. [0036] Moreover, the first and second stepped portions 16A and 16B extend to the rotary shaft direction L, respectively, and are disposed on the whole surface, for example, of a portion considered to be collided by the high-speed flow. The blow-out air velocity is distributed in the rotary shaft direction L, and the sizes of the swirls generated by the stepped portions 16A and 16B are also changed along the rotary shaft direction L. Thus, the pressure fluctuations are alleviated in the rotary shaft direction L, and the noise can be further reduced. Also, the stepped portion 16 is formed by consecutively providing a plurality of steps: five steps in Figs. 10 and 11, for example. Thus, the pressure fluctuations of the blow-out flow are gradually diffused toward the blow-out port 3 in the blow-out region E2, and the noise can be further reduced. [0037] Particularly, the stepped portions 16A and 16B are not formed in a portion B where the blow-out air velocity is low. If the blow-out air velocity is low, the noise caused by collision against the guide wall 10 does not matter much. If the stepped portion 16 is formed in this portion, the flow might be disturbed by the generated swirl. Thus, in this configuration example, the first and second stepped portions 16Aand 16B are disposed only in portions where the blow-out flows are at a high speed so as to reduce the noise caused by the high-speed flow. [0038] Depending on the configuration of the upstream side of the impeller 8a, the distribution of the blow-out air velocity V from the impeller 8a might become the one shown in Fig. 12. In Fig. 12, the horizontal direction indicates the rotary shaft direction L of the impeller 8a, while the vertical direction indicates the air velocity V. At this time, too, by providing the stepped portion 16 in which a plurality of steps are consecutively provided in a stepped shape in the portion where the blow-out flow is at a high speed or the guide wall 10 in the portion where the blow-out air velocity V becomes Vs or more, for example, the noise caused by the high-speed flow can be reduced. Here, since the value Vs as the threshold value is different also depending on an air feeding amount of the cross flow fan 8, [0039] In the above, for convenience of the explanation, the stepped portion 16 is assumed to be disposed in a portion where the blow-out air velocity V becomes the predetermined air velocity Vs or more. This predetermined air velocity value Vs is different depending on the sizes of the air conditioner and the cross flow fan and the configuration of an air path. Thus, they cannot be set uniformly but can be set empirically, experimentally or through simulation. Also, since the blow-out air velocity becomes the lowest at the both end portions in the rotary shaft direction L, a value not less than an intermediate value of the air velocity at the both end portions and the air velocity of the fastest portion, for example, may be set as Vs. [0040] As described above, by providing the inlet 2 through which the indoor air is sucked, the heat exchanger 7 that exchanges heat with the sucked indoor air, the blow-out port 3 through which the heat-exchanged indoor air is blown out into the room, the blower 8 having the impeller 8a, disposed on the downstream side of the heat exchanger 7 between the inlet 2 and the blow-out port 3 and rotated and driven by the motor 12, with the longitudinal direction of the air conditioner main body 1 as the rotary shaft direction L and feeding the indoor air from the inlet 2 to the blow-out port 3, the stabilizer 9 that separates the suction-side channel E1 on the upstream side of the impeller 8a and the blow-out-side channel E2 on the downstream side from each other and forms the front face side of the blow-out-side channel E2 from the impeller 8a to the blow-out port 3, the spiral guide wall 10 that forms the rear face side of the blow-out-side channel E2 from the impeller 8a to the blow-out port 3, and the stepped portion 14 disposed at least in a part of the guide wall 10 and having a plurality of the steps 14A, 14B, 14C, 14D, and 14E, each indented substantially in a triangular shape in the section perpendicular to the rotary shaft O of the impeller 8a and extending in the rotary shaft direction L, and forming steps in a direction in which the blower 8 feeds the air, such an advantage is exerted that an air conditioner in which separation of the flow on the surface of the guide wall 10 is suppressed, and the pressure fluctuations are diffused so as to lower the noise can be obtained. [0041] Also, on the section perpendicular to the rotary shaft O of the impeller 8a, the steps are configured such that the upstream-side end portion of one step in the stepped portion 14 is made the step start portion 14a, the portion indented to the deepest substantially in the shape of a triangle of the step is made the step deepest portion 14b, the downstream-side end portion of the step is made the step end portion 14d, and the relationship among the length C1 connecting the rotation center O of the impeller 8a to the step start portion 14a, the length C2 connecting the rotation center O of the impeller 8a to the step deepest portion 14b and the length C3 connecting the rotation center O of the impeller 8a to the step end portion 14d is C1 < C2 < C3, so the ventilation resistance can be reduced without disturbing the flow in the vicinity of the guide wall 10, and such an advantage is exerted that an air conditioner that can reduce the power consumption can be obtained. [0042] Also, on the section perpendicular to the rotary shaft O of the impeller 8a, the steps are configured such that the upstream-side end portion of one step in the stepped portion 14 is made the step start portion 14a, the portion indented to the deepest in a substantially triangular shape of the step is made the step deepest portion 14b, the downstream-side end portion of the step is made the step end portion 14d, and the relationship between the length h connecting the step start portion 14a to the step deepest portion 14b and the length S connecting the step deepest portion 14b to the step end portion 14d is h