To reduce vibration or noise occurring from an electromagnetic pump by reducing the weight of a piston jointed to the plunger of the electromagnetic pump.

A guide pipe 7 is fixed in an electromagnetic coil 2, and an electromagnetic plunger 10 is stored in the guide pipe 7 and is reciprocatably supported by springs 11, 12. A piston 17 facing a pump room 18 is jointed to the electromagnetic plunger 10, an inlet value is provided on the upstream side of the pump room 18, and a delivery valve 21 is provided on the downstream side respectively, and the volume of the pump room 18 is changed by the reciprocation of the piston 17. The piston 17 is constituted of a cylindrical member 17a and a detent plug 17b which blocks the opening end part of the cylindrical member 17a to reduce the weight of the piston. The piston 17 may be constituted of a member and a charging member with mass smaller than that is charged in the cylindrical member.