An apparatus for mounting an electromagnetic unit on a frame includes a mounting recess at the bottom of the main body of the electromagnetic unit, a guide recess which is communicated with the mounting recess at one side thereof so that it is normal to the mounting recess, and a slidable member which is slidably inserted into the guide recess and normally biased toward the mounting recess by means of a spring supported by a projection disposed in the guide recess, the improvement comprising a stopper disposed in a hole formed in the slidable member, which opposes the spring bearing in the guide recess. The stopper in the hole also serves as a spring guide. The spring is disposed between the stopper in the hole and the length a of the slidable member determined by guide projection formed at the guide recess, the movement length b of the slidable member restricted by the stopper and the projection length c of the front end of the slidable member which projects into the mounting recess is preset so that a>b>c.