To reduce the flow resistance of an axial flow pump during a trip and to increase the area of a passage in an impeller.

A cylindrical rotor is composed of an impeller 38 fixed to an impeller shaft 37 and a rotor cylinder 39 integrally fixed to the impeller shaft 37 so as to enclose the outside of the impeller 38. An annular stator 40 having an insulated coil therein is arranged so as to surround the cylindrical rotor with a clearance. The annular stator 40 is fixed to the inside surface of a cylindrical pump casing 42. A radial bearing 43 and a thrust bearing 44 are arranged on the upper portion of the stator 40. A diffuser 46 is arranged to the lower portion of the stator 40 via an inner annular member 45. A radial thrust bearing 47 is arranged on the upper surface of the diffuser 46. The lower end portion of the impeller shaft 37 is mounted on the radial thrust bearing 47.