PURPOSE: To prevent the drastic pressure change of a variable displacement type vane pump, by connecting a large-diameter piston for increasing the pump capacity to its maximum to a pump discharge circuit via a sequence valve and a check valve and a restriction disposed in parallel to each other.

CONSTITUTION: The pressure in a pump discharge circuit 8 is acted to a piston 6 via a sequence valve 11 and a check valve 12. When the pressure of the discharge circuit 8 exceeds a prescribed pressure, the position of the sequence valve 11 is shifted and tank pressure is acted to the piston 6. Resultantly, a cam ring 4 is pushed by the piston 6 in the direction descreasing the capacity of the pump. However, since the back pressure of the piston 6 is released gradually to a tank through a restriction 13, excessive shifting of the cam ring 4 can be prevented. Therefore, it is enabled to prevent drastic pressure change at the time of changing the capacity of a variable displacement type vane pump.