PURPOSE: To improve pump discharge efficiency and responsiveness by performing bleed of air in a pressure operating chamber.

CONSTITUTION: Positioning pins 41 and 42 are extended through the outer peripheries of side plates 32 and 33 and cam rings 31A and 31B and the ends on one side thereof are fixed to a pump housing wall 11. The positioning pipe 41 and 42 are a hollow pipe body and the ends on one side thereof are opened in a delivery space 11a formed in an annular shape around a rotary shaft 2 in the pump housing wall 11 and the ends on the other side thereof are communicated with a pressure operation chamber 13A. Flow cut-out plates are arranged to the edges of the openings to a delivery space 11a of the positioning pins 41 and 42 and flow cut-out plates for delivery fluid flowing in a peripheral direction in the space 11a are arranged such that one cut-out plate is located in a downstream position in one opening 411 edge and the other cut-out plate is located in an upper stream position in the other opening edge 421.