In a flow rate controller for use in a power steering apparatus used in automobiles, etc, a load pressure responding valve (24) equipped with a variable throttle (45) which causes a spring chamber of a flow rate regulating valve to communicate with the low pressure side when the load is light and cutting off the communication of the spring chamber with the lower pressure side in response to the load pressure which rises due to the steering operation is assembled inside a union (17) having a delivery port for sending the working oil the flow rate of which is controlled by the flow rate regulating valve to a control valve. Accordingly, the saving of energy for reducing the flow rate of the working oil to be supplied to the control valve when the load is light is accomplished without substantially changing the pump housing.