A pump casing has two external communication holes communicating with an outside. A partition member partitioning an interior of the pump casing into a first space and a second space. The first space communicates with the two external communication holes. The partition member have two internal communication holes communicating the first space with the second space. A first rotor member is rotatably accommodated in the first space. A second rotor member is rotatably accommodated in the second space. A torque switching unit is configured to switch between transmission of a running torque selectively to the first rotor member and transmission of the running torque to both the first rotor member and the second rotor member.