To reduce a pump capacity as well as to carry out a booster operation securely, even when a brake and a steering are operated simultaneously.

When a brake and a steering are operated simultaneously, in the condition the liquid pressure is accumulated in an accumulator 31 exceeding a specific value, and a flow rate limit valve 34 is set at a flow rate nonlimiting position I, the liquid pressure of the accumulator 31 is used to a brake boosting operation by a booster 28, and an operating liquid discharged from a pump 8, and not throttled by the flow rate limit valve 34 is used to a steering boosting operation by a power steering device 7. Consequently, since a sufficient operating liquid is fed to the power steering device 7 even in such a condition, two boosting operations are carried out securely at a time, the capacity of the pump 8 can be reduced, furthermore, both operations give no influence each other, and no shock is generated to a handle 6.