PURPOSE: To provide linear in-and-out-flow of liquid to a pump mechanism for improving efficiency in high speed by supporting a motor rotor on an exciting coil iron core of a AC motor to fix a cylindrical rotor having thrust blades to the inner periphery of the motor rotor.

CONSTITUTION: An AC motor has a exciting coil 2 and a motor rotor 5 which is supported by an iron core 3 of said coil such that a cylindrical rotor 6 having spiral projections 6a of thrust blades is fixedly fitted in the inner periphery of the motor rotor 5. When alternate current is applied to the exciting coil 2, the motor rotor 5 supported between flanges 3a of the coil iron core 3 is rotated to rotate the cylindrical rotor 6 integral with said rotor 5 so that liquid in said rotor 6 is given thrust by the spiral projections 6a to be accelerated and transferred from the input side pipe 9a to the outlet side pipe 9b. Since conversion of direction to give the thrust to liquid is minimized, the efficiency of transferring liquid in high speed is improved to provided a compact pump.