A variable oil pump capable of rapidly ejecting a required amount of working fluid using an oil pressure of the working fluid generated according to an engine RPM, and improving a lubrication effect to improve engine efficiency. Also described is a variable oil pump, in which a gap is provided between a plunger and a cylinder to easily operate the plunger using an oil pressure output from an oil pump, enabling more rapid supply of a required amount of oil using an oil pressure varied according to variation in an engine RPM. A variable oil pump is described in which the plunger is perpendicularly operated with respect to a flow direction of the working fluid, such that the plunger can be operated in a direction in which a pressure of the working fluid is applied to operate the oil pump.