Abstract: An electromagnetic pump having a pressure adjusting function that holds discharge pressure constant; a decompression valve for throttling an outflow is provided in the path of the discharge side and this decompression valve is displaced by a pressure receiving plunger to which the pressure of the discharge side is applied. The pressure receiving plunger is slidably provided in a cylinder, and a pressure adjusting spring facing the pressure receiving plunger of the cylinder is disposed in the chamber located on the opposite side of the decompression valve; a return path communicating with a suction side of the electromagnetic pump is formed in the chamber. The pressure is adjusted by the decompression valve, and the fluid leaking into the chamber located on the opposite side of the decompression chamber of the cylinder is returned to the suction side by means of the return path.