A shaft is press-fit into the valve member or the plunger of an electromagnetic valve to transmit the axial movement of the plunger to the valve member. A diameter reducing mechanism is provided for reducing the diameter of at least the press-fit portion of the shaft so that the diameter of the shaft is decreased by a press-fitting force applied to the shaft by the valve member and/or plunger. Deformation due to the press-fitting process is absorbed by the shaft, so deformation of the valve member and/or plunger is inhibited. Accordingly, it is unnecessary to give a large margin to a plunger side air gap, and magnetic efficiency can be improved. Also, two chambers on both axial sides of the plunger can communicate with each other through a clearance provided by the C-shaped cross-section, an inner hole and a penetration hole of the shaft. Therefore, it is unnecessary to form any separate groove or hole in the plunger for respiration.