Abstract: A flow rate control device for a pump includes a housing, a choke tubular passageway connected between a pump pressure chamber and an output chamber, a spool valve which is slidably provided in the housing, and which has both ends exposed in the pump pressure chamber and the pressure reducing chamber, respectively, the spool valve causing a pressure medium to flow from the pump pressure chamber into the by-pass port as much as the spool valve slides in an axial direction thereof. In the device, the choke tubular passageway is formed in a central shaft member arranged in the housing, and a sleeve member is provided around the central shaft member, the sleeve member being moved, from the pump pressure chamber towards the pressure reducing chamber, with respect to the central shaft member, in such a manner as to change the opening area of the choke tubular passageway.