A steering speed-computing section (81) to differentiate a steering angle of a steering wheel from a steering angle sensor (18) to compute the steering speed signal, a low-pass filter (82) to cut high frequency components in the steering speed signal to output a correction steering speed signal, a switching section (87) to switch the cut-off frequency in the low-pass filter to be higher at the time of determining a high-speed steering condition, and a flow quantity-computing section (85) to compute a target flow quantity supplied to a power steering output section (8) based on the steering angle signal and the correction steering speed signal are provided to control a flow quantity of an operating oil supplied to the power steering output section (8) for the target flow quantity.