PURPOSE: To obtain a tow-throw trochoid pump in small-sized and lightweight form by arranging an annular rotor which has the internal and external gears for the meshing with an external-gear rotor and an internal-gear rotor and carries out pumping action, between the both rotors.

CONSTITUTION: The second annular rotor 14 which has a shaft in eccentric position for the shaft of the third rotor 15 and carries out trochoid pump action through the meshing with the internal gear of the third rotor 15 is arranged onto the inner periphery of the third rotor 15 having the internal gears. While, the first rotor 13 which has a shaft in eccentric position for the shafts of the second rotor 14 and the third rotor 15 and carries out trochoid pump action through the meshing of the external gear with the internal gear of the second rotor 14 is arranged on the inner periphery of the second rotor 14. Therefore, the separate pump chambers are formed onto the inner and outer peripheral sides of the second rotor 14, and the function of two units of pumps can be obtained by only one unit of pump, and a two-throw trochoid pump can be made small-sized and lightweight.