To sufficiently protrude a vane by communicating each groove with another one or more groove via a communication passage in a device in which vanes are fitted in a plurality of grooves formed on the outer peripheral surface of a rotor.

A vane pump is provided wherein at the time of rotation of a rotor 2, each vane 3 repeats its projecting and retracting actions to each groove 7 by the aid of the centrifugal force thereof, and fluid taken in from an inlet 5 in a working space 4 between the vane 3 and the outer wall of the rotor 2 is boosted in its pressure and discharged from a discharge port 6. In such the pump bottom spaces 9 of the grooves 7 positioned differently at the angle of 180 degrees among the four grooves formed in the rotor 2 are mutually communicated through a communication passage 10. Accordingly, the bottom space 9 where the volume increases is prevented from being subjected to vacuum and the vanes 3 are made to protrude. Since the reduced volume of the bottom space 9 where the volume is decreased is transfered as it is to the bottom space 9 where the volume is increased the vane 3 can be protruded surely even if a sufficient centrigal force is not obtained.