To provide a cascade pump reducing pressure loss and improving pump efficiency.

A roughly arc shape pump passage 30 formed by a casing main body 21 and a casing cover 22 consists of an arc passage part 31, an outlet passage part 32 and a connection passage part 33. An inner wall 41 of the casing main body 21 and an inner wall 42 of the casing cover 22 are formed in curve shapes in the connection passage part 33 connecting the arc passage part 31 communicating to a suction port and the outlet port passage part 32 communicating to the outlet 26. Consequently, changes of cross section area of a fluid passage gets small from the arc passage part 31 to the outlet passage part 32. Consequently, cross section area of the fluid passage does not quickly expands and pressure loss of fluid is reduced in the connection passage part 33. Consequently, pressure of delivered fluid is increased and pump efficiency can be improved.