The present invention mainly relates to a yarn withdrawal device adapted to withdraw a yarn from a package . 2.Description of the Related Art A yarn withdrawal device arranged in proximity to a package and adapted to withdraw a yarn of the package to perform, for example, yarn joining operation is conventionally known. This type of yarn withdrawal device is disclosed in Japanese Patent Application Laid-open No. 2014-125348 (patent document 1), Japanese Utility Model Application Laid-open No. H5-5769 (patent document 2) , and German Patent Application Publication No. 2426724 (patent document 3). Patent document 1 discloses a yarn withdrawal device formed with one slit for inj ecting compressed air . Airflow generated by the compressed air inj ected from the slit flows along an outer wall surface of the yarn withdrawal device. Since the outer wall surface is arranged in proximity to the package, a yarn is withdrawn from the package by the airflow. Patent documents 2 and 3 disclose yarn end withdrawal devices having a structure in which two nozzle tubes are arranged in an axial direction of the package. A plurality of nozzle holes are formed in each of the two nozzle tubes. A yarn entangled with the surface of the package can be detached (separated, removed, lifted) from the package by injecting the air from such nozzle holes. BRIEF SUMMARY OF THE INVENTION However, in the yarn withdrawal device of patent document 1, a range in which the airflow is acted on the package is not sufficient as only one slit is provided. As a result, there is a possibility that the yarn may not be withdrawn from the package. Furthermore, in patent documents 2 and 3, the strength of the airflow may become uneven in the axial direction of the package as the air is injected from the nozzle holes. As a result, there is a possibility that the yarn may not be withdrawn from the package. It is a main obj ect of the present invention to provide a yarn withdrawal device having a high possibility of succeeding in withdrawal of a yarn from a package. A yarn withdrawal device adapted to withdraw a yarn from a package, the yarn withdrawal device comprises a first injecting section in which a first slit is formed and adapted to generate a first airflow by air being injected from the first slit; and a second injecting section in which a second slit is formed along a longitudinal direction of the first slit and adapted to generate a second airflow by air being injected from the second slit, the second airflow being an airflow flowing in a direction different from a direction of the first airflow. A yarn withdrawal device adapted to withdraw a yarn from a package, the yarn withdrawal device comprises a main body part; a first injecting section including a first spacer portion and a first cover portion, a first slit being formed by the first spacer portion being arranged between the first cover portion and the main body part, the first injecting section being adapted to generate a first airflow by air being injected from the first slit; and a second injecting section including a second spacer portion and a second cover portion, a second slit being formed by the second spacer portion being arranged between the second cover portion and the first cover portion, the second injecting section being adapted to generate a second airflow by air being injected from the second slit. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front view of an automatic winder according to an embodiment of the present invention; FIG. 2 is a side view illustrating a schematic structure of a winding unit; FIG. 3 is a perspective view of an outer appearance of a yarn withdrawal device; FIG. 4 is an exploded perspective view of the yarn withdrawal device; FIG. 5 is a side view of the yarn withdrawal device and a package; and FIG. 6 is a side cross-sectional view of a proximity of a first slit and a second slit. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Exemplary embodiments of the present invention will be described in detail below with reference to the accompanying drawings. As illustrated in FIG. 1, an automatic winder (yarn winding machine) 1 includes a plurality of winding units 10 arranged in line, a doffing device 5, and a main control device 100. Each of the winding units 10 is adapted, while traversing a yarn 2 0 unwound from a yarn supplying bobbin 21, to wind the yarn 20 around a winding tube 22 supported by a cradle (winding tube supporting section) 23 to form a package 30. When the package 30 is fully wound in any of the winding units 10, the doffing device 5 travels up to the position of the relevant winding unit 10, discharges the fully wound package 30 from the winding unit 10 (doffing operation), and supplies a winding tube 22, around which the yarn 20 is not wound, to the winding unit 10. The main control device 100 includes a machine setting section 101 and a machine display section 102 . The machine setting section 101 can carry out setting with respect to each of the winding units 10 by enabling an operator to input predetermined set values, select an appropriate control method, and the like. The machine display section 102 can display a winding status of the yarn 20 in each of the winding units 10, content of trouble that occurred, and the like. A structure of the winding unit 10 will now be specifically described with reference to FIG. 2. The winding unit 10 includes a yarn unwinding assisting device 12, a tension applying device 13, a yarn joining device 14, a clearer 15, and a winding section 18 arranged in such order from the yarn supplying bobbin 21 on a yarn travelling path between the yarn supplying bobbin 21 and the winding tube 22. The yarn unwinding assisting device 12 includes a regulating member 25 placed over a core tube of the yarn supplying bobbin 21. The yarn unwinding assisting device 12 assists in the unwinding of the yarn 20 from the yarn supplying bobbin 21 by lowering the regulating member 25 accompanying the unwinding of the yarn 20 from the yarn supplying bobbin 21. The regulating member 25 is brought 5 into contact with a balloon formed at an upper part of the yarn supplying bobbin 21 by rotation and a centrifugal force of the yarn 20 unwound from the yarn supplying bobbin 21 to control the balloon to an appropriate size, thus assisting the unwinding of the yarn 20. A sensor (not 10 illustrated) adapted to detect a chase portion (upper end of yarn layer) of the yarn supplying bobbin 21 is arranged in proximity to the regulating member 25. When this sensor detects lowering of the chase portion, the regulating member 25 is lowered by, for example, an air cylinder (not 15 illustrated). The tension applying device 13 applies a predetermined tension on the travelling yarn 20. For example, a gate-type tension applying device, in which movable comb teeth are arranged with respect to fixed comb 20 teeth, is used as the tension applying device 13. The movable comb teeth can be swung by a rotary solenoid to cause the movable comb teeth to be in an engaged state or in a released state with the fixed comb teeth. Other than the gate type tension applying device, a disk-type tension 25 applying device, for example, can also be used as the tension applying device 13. The yarn joining device 14 joins a yarn 20 (lower yarn) from the yarn supplying bobbin 21 and a yarn 20 (upper yarn) from the package 30 when yarn cutting is performed upon 30 detection of a yarn defect by the clearer 15 or when yarn breakage occurs during the unwinding of the yarn 20 from 6 / 42 the yarn supplying bobbin 21. The yarn joining device 14 can be of a mechanical type or of a type that uses fluid such as compressed air. The clearer 15 includes a sensor (not illustrated) 5 adapted to detect, for example, the thickness of the yarn 20 and/or presence or absence of foreign substances in the yarn 20. The clearer 15 detects yarn defects, such as slub, by monitoring a yarn thickness signal output by the sensor. A cutter 39 is arranged in proximity to the clearer 15 to 10 cut the yarn 20 immediately when the clearer 15 detects a yarn defect. A lower yarn catching member 33 is arranged below the yarn joining device 14, and adapted to catch the lower yarn from the yarn supplying bobbin 21 and guide the lower yarn 15 to the yarn joining device 14. An upper yarn catching member (first catching member) 36 is arranged above the yarn joining device 14, and adapted to catch the upper yarn from the package 30 and guide the upper yarn to the yarn joining device 14. 20 The lower yarn catching member 33 is swingable with a shaft 34 as a center. The upper yarn catching member 36 is swingable with a shaft 37 as a center. Each of the lower yarn catching member 33 and the upper yarn catching member 36 is connected to an appropriate negative pressure source 25 (not illustrated). Thus, a suction flow can be generated at an opening of a distal end of the lower yarn catching member 33 to suck and catch the lower yarn with the lower yarn catching member 33. A suction flow can also be generated at an opening of a distal end of the upper yarn 30 catching member 36 to suck and catch the upper yarn with the upper yarn catching member 36. At least one of the lower 7 / 42 yarn catching member 33 or the upper yarn catching member 36 is not limited to a configuration of catching the yarn 20 by generating the suction flow, and may have a configuration of catching the yarn 20 using a member adapted 5 to clamp the yarn 20. The winding section 18 includes the cradle 23 adapted to detachably support the winding tube 22, and a contact roller 29 adapted to be rotatable while making contact with an outer peripheral surface of the winding tube 22 or an 10 outer peripheral surface of the package 30. The cradle 23 is supported to be swingable in a direction approaching the contact roller 29 and in a direction away from the contact roller 29. Increase in the diameter of the yarn layer of the package 30 accompanying 15 the winding of the yarn 20 on the winding tube 22 can be absorbed by the swinging of the cradle 23. The contact roller 29 is arranged to oppose the winding tube 22 and to make contact with the winding tube 22 or the package 30. Therefore, by rotating the contact 20 roller 29, the winding tube 22 or the package 30 can be rotated. A traverse groove (not illustrated) is formed on the outer peripheral surface of the contact roller 29, and the yarn 20 can be traversed within a predetermined width by the traverse groove. Accordingly, the winding unit 10 25 can wind the yarn 20 around the winding tube 22 while traversing the yarn 20 to form the package 30. The traverse method of the yarn 20 is not limited to the traverse groove, and may be a traverse mechanism (rod-type traverse device, arm-type traverse device, or 30 belt-type traverse device) independently arranged from the contact roller 29. In this case, in place of the 8 / 42 configuration in which the contact roller 29 is driven and the winding tube 22 or the package 30 is rotated following the rotation of the contact roller 29, the winding tube 22 or the package 30 may be driven and the contact roller 29 5 may be rotated following the rotation of the winding tube 22 or the package 30. A yarn withdrawal device 28 is arranged in proximity to the contact roller 29 and the package 30. The yarn withdrawal device 28 is a device adapted to withdraw the 10 yarn 20 from the package 30. When the yarn 20 between the yarn supplying bobbin 21 and the package 30 is disconnected, the yarn withdrawal device 28 injects air to generate an airflow to withdraw the yarn 20 from the package 30. A case in which the yarn 20 is disconnected includes, for example, 15 a case in which the yarn 20 is broken and/or a case in which the yarn 20 is cut with a cutter 39 upon detection of a yarn defect by the clearer 15, and the like. The timing for the yarn withdrawal device 28 to start the injection of air may be when the package 30 is rotating 20 in a reverse rotational direction (unwinding direction), which is a direction opposite to the winding direction, or when the package 30 stops rotating in the winding direction and starts rotating in the reverse rotational direction. The yarn withdrawal device 28 may inject air while the 25 package 30 decelerates from the state of rotating in the winding direction to prevent the yarn 20 from attaching to the package 30. Thus, the yarn withdrawal device 28 can more reliably withdraw the yarn 20 from the package 30. When withdrawing the yarn 20 from the package 30, the 30 winding section 18 reversely rotates the package 30. When failing in the withdrawal of the yarn 20 from the package 9 / 42 30, the reverse rotation of the package 30 is stopped, and the package 30 is rotated several times in the winding direction. In this case, the airflow may be injected from the yarn withdrawal device 28. Thus, when carrying out the 5 withdrawal of the yarn 20 from the package 30 the second time, the probability of withdrawal of the yarn 20 from the package 30 increases. The yarn 20 (upper yarn) withdrawn from the package 30 in such a manner is caught by the upper yarn catching member 36, and guided to the yarn joining 10 device 14 (second target position). The upper yarn guided to the yarn joining device 14 is joined with the lower yarn caught and guided by the lower yarn catching member 33 by the yarn joining device 14. The upper yarn catching member 36 is set such that 15 the suction force when sucking and catching the yarn 20 becomes greater than the suction force when guiding the sucked yarn 20 to the yarn joining device 14. Thus, the probability of failing in catching at the time of catching the yarn 20 can be lowered, and the probability of yarn 20 breakage at the time of guiding the yarn 20 can be lowered. However, the suction force of the upper yarn catching member 36 may be a constant suction force from the time of catching to the time of guiding. A structure of the yarn withdrawal device 28 will be 25 described in detail with reference to FIGS. 3 to 6. As illustrated in FIG. 3, the yarn withdrawal device 28 has a substantially rectangular parallelpiped shape, and includes a first outer surface 28a and a second outer surface 28b. As illustrated in FIG. 5, the yarn withdrawal 30 device 28 is arranged such that the first outer surface 28a and the second outer surface 28b are located in proximity 10 / 42 to the package 30. The first outer surface 28a is arranged at an angle along the surface of the package 30 (angle close to a tangential direction of the package 30). The yarn withdrawal device 28 detaches the yarn 20 from the package 5 30 and feeds the yarn 20 toward the second outer surface 28b by the airflow (specifically, first airflow 91 and second airflow 92 to be described later) generated on the first outer surface 28a to withdraw the yarn 20 from the package 30. The second outer surface 28b is arranged at 10 an angle to lie along a radial direction of the package 30. The second outer surface 28b is located on a downstream side of the first outer surface 28a in a flow direction of the airflow. The yarn withdrawal device 28 guides the yarn 20 detached from the package 30 along the second outer surface 15 28b to an opening (catching position, first target position) of the upper yarn catching member 36 arranged at a catching position (position of chain double dashed line in FIG. 2). As illustrated in FIG. 3, the yarn withdrawal device 20 28 includes a main body part 40, a first injecting section 50, and a second injecting section 60. In the following description, as illustrated in FIGS. 3 and 4, an axial direction of the package 30 (winding tube 22) is referred to as “package axial direction”. When seen in the package 25 axial direction (i.e., in side view such as FIG. 5), a direction along the first outer surface 28a (more precisely, a direction along a portion not formed with an inclined surface) is referred to as a “first direction”. A direction perpendicular to the first direction when seen in the 30 package axial direction is referred to as a “second direction”. 11 / 42 The main body part 40 is attached in proximity to the winding section 18 by an attachment mechanism (not illustrated). The main body part 40 may be movable between a position in proximity to the package 30 and a position 5 spaced apart from the package 30. An air supplying tube 81 adapted to supply compressed air is attached to the main body part 40. The main body part 40 is provided with a first air supplying path 41, a second air supplying path 42, a curved surface 43, and a guiding section 45. 10 The first air supplying path 41 and the second air supplying path 42 are spaces formed inside the main body part 40, and are paths through which the compressed air supplied through the air supplying tube 81 flows. The compressed air flows along the second direction 15 (specifically, toward a side where the first injecting section 50 and the second injecting section 60 are arranged) through the first air supplying path 41 and the second air supplying path 42. The first air supplying path 41 is formed on one side (specifically, a side close to the second 20 outer surface 28b) of the second air supplying path 42 in the first direction. The compressed air supplied through the first air supplying path 41 is injected from the first injecting section 50 to generate the first airflow 91. The compressed air supplied through the second air supplying 25 path 42 is injected from the second injecting section 60 to generate the second airflow 92. The first air supplying path 41 and the second air supplying path 42 are not divided into different sections by a partition and the like, and are connected. Therefore, the first airflow 91 and the 30 second airflow 92 have a common air supplying path. The curved surface 43 is a surface exposed to the 12 / 42 exterior of the yarn withdrawal device 28. The curved surface 43 is a surface curved to smoothly connect the first outer surface 28a and the second outer surface 28b and to project outward. 5 The guiding section 45 is provided on the second outer surface 28b. The guiding section 45 is adapted to guide the yarn 20 withdrawn from the package 30 by the yarn withdrawal device 28 toward the first target position. The guiding section 45 includes two members protruding out in 10 the first direction from respective ends in the package axial direction (package width direction) of the second outer surface 28b. One of the two members is provided with a first guiding surface 45a, and the other member is provided with a second guiding surface 45b. 15 The first guiding surface 45a and the second guiding surface 45b are arranged to face toward a center side in the package width direction so as to face one another. The first guiding surface 45a and the second guiding surface 45b are surfaces substantially perpendicular to the second 20 outer surface 28b. An interval between the first guiding surface 45a and the second guiding surface 45b increases toward the first outer surface 28a (toward the curved surface 43). In other words, the interval between the first guiding surface 45a and the second guiding surface 45b 25 becomes narrower toward the downstream side in the guiding direction of the yarn 20. At a position located closer toward the downstream side in the guiding direction of the yarn 20, the first guiding surface 45a and the second guiding surface 45b are respectively inclined so as to 30 become closer toward the center side in the package axial direction. 13 / 42 As illustrated in FIG. 3, the first target position is not the center in the package axial direction, but is closer to the first guiding surface 45a (L1