PURPOSE: To obtain a pump of high total adiabatic efficiency by housing a male rotor having a sheet of blade, integrally rotated with a rotary hollow body, and a female rotor having a sinking part, to which the blade of the male rotor is fitted while sinking from an external peripheral surface of this female rotor, in a casing.

CONSTITUTION: A male rotor 1 having a sheet of blade 2, integrally rotated with a rotary hollow body 6 while being brought into close contact with the peripheral surface of a fixed hollow body A, and a female rotor 8 having a sinking part 10, to which the blade 2 of the before-mentioned rotor 1 is fitted while sinking from an external peripheral surface brought into close contact with a casing internal peripheral surface, are housed in a casing rotatably in an opposite direction to each other. Fluid in an operating chamber 12, interposed by the blade 2 of the male rotor 1 and the female rotor 8, is delivered to the rotary hollow body 6 through a delivery port 5, formed in the fixed hollow body 14, and an opening/closing port 7 formed in the rotary hollow body 6. Constitution is provided such that a cylindrical surface, formed in the bottom part of the sinking part 10 of the female rotor 8, and a cylindrical surface, formed in the blade 2 of the male rotor 1, are brought into close contact with each other.