Provided are a hydraulic pump 7, an electromagnetic flow rate control valve 2 that controls the flow rate of hydraulic oil supplied from the hydraulic pump 7 to a power steering device PS, and a pressure compensating valve 4 that maintains a fixed pressure difference between upstream and downstream sides of the electromagnetic flow rate control valve 2 and bypasses an excess flow rate. The electromagnetic flow rate control valve 2 maintains a predetermined initial opening when a control current is zero, while an opening of the electromagnetic flow rate control valve decreases to become a minimum opening when the control current increases from zero, and the opening gradually becomes larger toward a maximum opening when a predetermined control current is exceeded.