An oil pump unit with a variable flow rate includes: an oil pump having an intake port and a discharge port and accommodating a pump rotor; and an oil path switching valve having oil inlets and oil outlets and opening/closing oil pressure return holes communicating with the discharge port, in which the oil path switching valve and the oil pump are separately disposed, the intake port and the discharge port are open to valve-mounting surfaces formed at the oil pump, and oil inlets and the oil outlet are open to body-mounting surfaces matching with the valve-mounting surfaces of the oil path switching valve.