Abstract: A first communication groove (38) extending from a start point of a discharge port (36) in a direction opposite to rotation direction of vanes (22) is formed. A first end portion (38E) of this groove is connected to the start point of the discharge port (36). When a front-side vane in a rotation direction of a driving shaft (11) is positioned at the start point of the discharge port (36), a second end portion (38S) of the groove is positioned at a rear side in the rotation direction with respect to a rear-side vane coming immediately after the front-side vane, and communicates with a suction port (35). A part of working fluid in a front-side pump chamber (27-1) can therefore be introduced into a rear-side pump chamber (27-2) that communicates with the suction port (35), thereby lessening excessive pressure increase of the front-side pump chamber (27-1) and suppressing pulsation phenomenon.

Abstract: A groove (38) extending from a start point of a discharge port (36) in a direction opposite to rotation direction of a vane (22) is formed. A first end portion (38E) of this groove is connected to the start point of the discharge port (36). When a front-side vane (22) in a rotation direction of a driving shaft (11) is positioned at the start point of the discharge port (36), a second end portion (38S) of the groove is positioned at a rear side in the rotation direction of the driving shaft (11) with respect to a rear-side vane (22), and communicates with a suction port (35). A part of working fluid in a front-side pump chamber (27) can be introduced into a rear-side pump chamber (27) that communicates with the suction port (35). Excessive pressure increase of the front-side pump chamber (27) can be lessened, thereby suppressing pulsation phenomenon.