In an impeller 11, an inlet portion and an outlet portion are provided at one end side and the other end side in the axial direction, respectively. An inlet 29 is formed in the lower part of the inlet portion, and an outlet is formed in the side face of the outlet portion. The inlet portion and the outlet portion are partitioned by a flange portion 40. The impeller 11 includes a primary vane 36 and a secondary vane 38. The primary vane 36 defines a spiral primary channel 35 that connects the inlet 29 and the outlet. The secondary vane 38 is formed in a shape that a part of the outer periphery of the outlet portion is gouged inward so as to define a secondary channel 37 connected to the primary channel 35 and extending circumferentially around the outer periphery.