To provide a magnet switch for a starter which surely separates contacts away and facilitates assembly.

The magnet switch includes a plunger with a shaft, a return spring for the plunger, a fixed contact, a shaft with a movable contact, and an exciting coil. The shaft with the movable contact is hollow and has a polygonal or elliptical window for inserting the plunger shaft on its end face. The plunger shaft has a protrusion having the same shape as the insertion window on its end face, which is inserted into the plunger shaft insertion window and rotationally locked. This allows supplying the inertial force upon plunger movement generated by the biasing force of the return spring for the plunger when the current to the exciting coil is cut off to the shaft with the movable contact through the plunger shaft. It is thereby possible to positively separate the contacts for certain without increasing assembly process.