To provide a displacement pump constituted to generate pumping action using rotation and swinging motion.

This displacement pump 1 is provided with a disc-like rotor 2 and a housing 3. An upper face 2a of the disc like rotor 2 is provided with two projecting parts 2b, 2b with a phase difference of 180° with respect to a circumferential direction, and a lower face 2c is provided with two projecting parts 2c, 2c with a phase difference of 90° from the upper face 2a with respect to the circumferential direction. The housing 3 is provided with a rotor chamber 3a for accommodating the rotor 2, and an input port 5 and an output port 6 communicating with the rotor chamber 3a. Inner surfaces 3b, 3c of the rotor chamber 3a are set to surround the moving range of the rotor 2 when putting the rotor 2 in swinging motion around the center C as a fulcrum and rotation of one half of the angular velocity of the swinging motion, around the centerline X as an axis.