Title of Invention PROPELLER FAN, AIR-SENDING DEVICE, AND REFRIGERATION CYCLE DEVICE Technical Field [0001] The present invention relates to a propeller fan including a shaft portion and a blade on an outer peripheral side of the shaft portion, an air-sending device, and a refrigeration cycle device. Background Art [0002] Patent Literature 1 describes an impeller of an air-sending device. The impeller of an air-sending device includes a blade having a lower pressure surface in which plural substantially circular dimples are formed. The dimples have a diameter of 1 mm to 20 mm, and a depth of 5% to 50% of the thickness of the blade. Citation List Patent Literature [0003] Patent Literature 1: Japanese Unexamined Patent Application Publication No. 3-294699 Summary of Invention Technical Problem [0004] A blade is typically more susceptible to flow separation at its trailing edge than at the leading edge. Thus, the blade having the recesses may promote flow separation with the recesses at the trailing edge of the blade. The impeller of an air-sending device of Patent Literature 1 thus has a problem that the efficiency of an air-sending device may be degraded. [0005] The present invention has been attained to solve the above problem and aims to provide a propeller fan, an air-sending device, and a refrigeration cycle device that can improve the efficiency. Solution to Problem [0006] A propeller fan according to an embodiment of the present invention includes a shaft portion disposed on a rotation axis; and a blade disposed on an outer peripheral side of the shaft portion, and including a leading edge and a trailing edge. The blade includes a negative pressure surface in which a plurality of recesses are formed, and the plurality of recesses include a first recess and a second recess disposed on the trailing edge side than the first recess in a circumferential direction about the rotation axis at a center. The first recess has a depth larger than a depth of the second recess. An air-sending device according to an embodiment of the present invention includes the propeller fan according to any one of the above embodiments of the present invention; an air-sending device motor that drives the propeller fan; and a support element that includes a motor fixing portion to which the fan motor is fixed and a support portion that supports the motor fixing portion. When viewed in a direction parallel to the rotation axis, the plurality of recesses are formed only in an inner peripheral side of a minimum circle that surrounds the motor fixing portion about the rotation axis at a center. A refrigeration cycle device according to an embodiment of the present invention includes the propeller fan according to any one of the above embodiments of the present invention. A refrigeration cycle device according to an embodiment of the present invention includes an air-sending device according to any one of the above embodiments of the present invention. Advantageous Effects of Invention [0007] According to embodiments of the present invention, the recesses disposed at the trailing edge in the circumferential direction are allowed to have a smaller depth, and can thus prevent promotion of flow separation at the trailing edge of the blade. This structure can thus improve the efficiency of a propeller fan. Brief Description of Drawings [0008] [Fig. 1 ] Fig. 1 is a back view of a structure of a propeller fan 100 according to Embodiment 1 of the present invention. [Fig. 2] Fig. 2 is a schematic cross-sectional view taken along line ll-ll of Fig. 1. [Fig. 3] Fig. 3 is a schematic cross-sectional view taken along line Ill-Ill of Fig. 1. [Fig. 4] Fig. 4 is a back view of a structure of a propeller fan 100 according to Embodiment 2 of the present invention. [Fig. 5] Fig. 5 is a front view of a related portion of an air-sending device 200 according to Embodiment 3 of the present invention. [Fig. 6] Fig. 6 is a back view of a related portion of the air-sending device 200 according to Embodiment 3 of the present invention. [Fig. 7] Fig. 7 is a back view of a structure of a propeller fan 100 according to Embodiment 3 of the present invention. [Fig. 8] Fig. 8 is a refrigerant circuit diagram of a structure of a refrigeration cycle device 300 according to Embodiment 4 of the present invention. [Fig. 9] Fig. 9 is a perspective view of an internal structure of an outdoor unit 310 of the refrigeration cycle device 300 according to Embodiment 4 of the present invention. Description of Embodiments [0009] Embodiment 1 A propeller fan according to Embodiment 1 of the present invention will be described. The propeller fan is installed in a refrigeration cycle device such as an air-conditioning apparatus, or a ventilator. Fig. 1 is a back view of a structure of a propeller fan 100 according to the present embodiment. As illustrated in Fig. 1, the propeller fan 100 includes a hollow cylindrical boss 10 (an example of a shaft portion), which is disposed on a rotation axis R and rotates about the rotation axis R, and plural plate-shaped blades 20, disposed on the outer peripheral side of the boss 10. The plural blades 20 are arranged at regular angular distances about the boss 10 at the center. A rotation direction of the propeller fan 100 is a counterclockwise direction, as indicated by arrow in Fig. 1. In Fig. 1, a surface of each blade 20 on the near side serves as a negative pressure surface 20a, and a surface of each blade 20 on the far side serves as a pressure surface 20b. The number of blades 20 is not limited to three. The plural blades 20 may be arranged at different angular distances about the boss 10 at the center. The shape of the boss 10 is not limited to a hollow cylindrical shape. [0010] Each blade 20 has a leading edge 21, a trailing edge 22, an outer peripheral edge 23, and an inner peripheral edge 24. The leading edge 21 is an edge portion located on the front side of the blade 20 in the rotation direction. The trailing edge 22 is an edge portion located on the rear side of the blade 20 in the rotation direction. The outer peripheral edge 23 is an edge portion located on the outer peripheral side of the blade 20 to connect the outer peripheral end of the leading edge 21 to the outer peripheral end of the trailing edge 22. The inner peripheral edge 24 is an edge portion located on the inner peripheral side of the blade 20 to connect the inner peripheral end of the leading edge 21 to the inner peripheral end of the trailing edge 22. The inner peripheral edge 24 is connected to the outer peripheral surface of the boss 10. The blade 20 is formed of resin. [0011] Each blade 20 has plural recesses 30 in the negative pressure surface 20a. In the present embodiment, the plural recesses 30 are formed only in a portion of the negative pressure surface 20a of the blade 20 near the inner periphery. The plural recesses 30 are circular or elliptic when viewed in a direction parallel to the rotation axis R. Here, the recesses 30 may have another shape such as a polygonal shape when viewed in a direction parallel to the rotation axis R. [0012] Fig. 2 is a schematic cross-sectional view taken along line 11-11 in Fig. 1. Fig. 2 is a cross-sectional view of the blade 20 in the circumferential direction about the rotation axis R at the center. Fig. 2 illustrates three recesses 30a, 30b, and 30c of the plural recesses 30. The up and down directions in Fig. 2 indicate the direction parallel to the rotation axis R, the upper side represents an upstream side of an airflow, and the lower side represents a downstream side of an airflow. The left and right directions in Fig. 2 indicate the circumferential direction about the rotation axis R at the center, the left side represents the side closer to the leading edge 21, and the right side represents a side closer to the trailing edge 22. Here, the same cylindrical surface about the rotation axis R as the center passes through the recesses 30a, 30b, and 30c, but not necessarily passes the centers of all the recesses 30a, 30b, and 30c. However, Fig. 2 illustrates cross-sectional shapes of the recesses 30a, 30b, and 30c on the assumption that they are taken by a cylindrical surface that passes all the centers. [0013] As illustrated in Fig. 2, each of the recesses 30a, 30b, and 30c has a chamfered opening end 31 formed in the negative pressure surface 20a, a cylindrical inner wall surface 32 extending from the opening end 31 in the direction parallel to the rotation axis R, and a substantially flat bottom surface 33. Among the three recesses 30a, 30b, and 30c, through which the same cylindrical surface about the rotation axis R as the center passes, the recess 30a (an example of a first recess) is located closest to the leading edge 21 in the circumferential direction about the rotation axis R as the center. In the present embodiment, the recess 30a is located closest to the leading edge 21 in the circumferential direction among all the recesses 30 formed in the negative pressure surface 20a of one blade 20. The recess 30b is located on to the trailing edge 22 side than the recess 30a in the circumferential direction. The recess 30c (an example of a second recess) is located on the trailing edge 22 side than the recesses 30a and 30b in the circumferential direction. However, the recesses 30a, 30b, and 30c are not necessarily disposed on the same circumference about the rotation axis R as the center. The blade thickness distribution of the blade 20 shows a larger blade thickness toward the leading edge 21, and a smaller thickness toward the trailing edge 22. [0014] The recess 30a has a depth of D1. Here, the depth of the recess 30 refers to a distance in the direction parallel to the rotation axis R from the center portion of the opening end 31 of the recess 30 to the bottom surface 33. A depth D2 of the recess 30c located on the trailing edge 22 side than the recess 30a is smaller than the depth D1 (D1>D2). In the present embodiment, the recesses 30 on the leading edge 21 side in the circumferential direction have larger depths, and the recesses 30 on the trailing edge 22 side in the circumferential direction have smaller depths. [0015] When the depth of each of the recesses 30a, 30b, and 30c at a portion on the leading edge 21 side than the center portion of the opening end 31 is denoted by Df and the depth of each of the recesses 30a, 30b, and 30c at a portion on the trailing edge 22 side than the center portion of the opening end 31 is denoted by Dr, the depth Df is larger than the depth Dr (Df>Dr). [0016] Each of the recesses 30a, 30b, and 30c has, in the cross section taken in the circumferential direction, a first opening end 31a at a portion on the leading edge 21 side and a second opening end 31 b at a portion on the trailing edge 22 side. A radius of curvature R1 of the first opening end 31a is smaller than a radius of curvature R2 of the second opening end 31b (0