An oil pump includes a capacity adjustment mechanism that changes the pump capacity by moving a tubular body in a tube radial direction, with a pump chamber formed between the tubular body and an outer circumference side of a rotor, a first spring biasing the tubular body in a direction in which pump capacity increases, a control valve that converts oil pressure of the oil pump into control pressure and causes the control pressure to act on the capacity adjustment mechanism, and a second spring biasing a valve body in order to set the control pressure in the control valve. The relationship of the biasing forces of the first and second springs is set so that pump capacity is set to maximum when the engine rotational speed is less than a predetermined value, and so that pump capacity is reduced when the engine rotational speed exceeds a predetermined value.