To attain an exact switching area of power steering fluid pressure computed from the current of a pump driving motor by correcting a switching point load value according to a power steering fluid temperature.

The output of a sum-block 122, which is obtained from motor current, and is the approximate value of power steering load compensated for power steering fluid temperature and a motor speed is provided in a nonlinear low-pass filter 124. The output of the low-pass filter is formed as one input to a function generator 126. The nonlinear low-pass filter 124 is formed to provide a different time constant from the changing value of power steering load. A fast time constant is provided to increase the motor current so as to conduct switching promptly from a standby condition, and is restricted so as not to generate noise at the time of switching like this.