To provide an electromagnetic switch for a starter which secures dust and water prevention in a moving core sliding part and a contact chamber, shown satisfactory sealability and assembling property, and attains reduction in cost, size and weight.

In an electromagnetic switch for a starter, a moving core 5 has a moving core main body 5a integrated with a stepped small diameter portion 5b having a shift lever engagement portion 5c at its end. A cup-like holder 6 has a flange 6a and a center hole 6b having an end to which rubber is baked to attach it. A contact portion 6c to which rubber is baked to attach it is formed on the surface of the flange 7a which is abutted against a plate 4 of a yoke 1 through that the moving core main body 5a slidably penetrates. A cover 9 is locked by a retaining ring 8 fitted in a retaining ring groove 7 formed on substantially a center portion of the stepped small diameter portion. A return spring 10 is elastically repulsively engaged between a flange portion 9a installed at an outer periphery of the cover 9 and the flange 6a.