When the coil is electrified, the static iron core generates electromagnetic attraction and pulls the moving iron core together. Because the contact system is linked with the moving iron core, the moving iron core drives three moving contacts to move simultaneously. The main contacts are closed, and the auxiliary normal closed contacts which are mechanically connected with the main contacts are disconnected, and the auxiliary normal open contacts are closed, thus the power supply is connected. When the coil is cut off, the suction disappears, and the moving iron core part is separated by the reaction force of the spring, so that the main contacts are disconnected, and the auxiliary normal closed contacts which are mechanically connected with the main contacts are closed, and the auxiliary normal open contacts are disconnected, thus cutting off the power supply.