To provide a cascade pump which can be started normally even without priming water.

In this cascade pump 1 comprising an impeller 22 having a large number of blades 35 on a circumferential edge part and rotatably accommodated in a casing 21, a flow passage 27 which is extended along a circumferential edge part of the impeller 22 with one side of a drain part 28 formed inside the casing 21 as a starting end and the other side as a terminating end, and a discharge port 34 communicated with the flow passage 27 at the terminating end, an inlet port 11 is provided on the inner side of the blades 35 of the impeller 22, and a suction space 12 which is expanded outwardly from the inlet port 11 and opened in the flow passage 27 on one side of the drain part 28 is formed on an inner circumferential surface of the casing 21.