Abstract: An electromagnet comprising an excitation coil wound as a solenoid and hag at least two windings which can be selectively supplied; a core fixedly mounted with respect to the coil, a movable core which can move axially with respect to the said coil, and an electric switch which can be actuated by the said movable core selectively to supply the two windings of the coil. The most important characteristic of the electromagnet is the fact that the switch includes a plurality of contact elements mounted fixedly with respect to the coil and the fixed core, and a plurality of movable contact elements carried by a small piston which can move axially with respect to the coil under the action of the said movable core.