PURPOSE: To shorten the release time of an armature without using an expensive material by hollowing out an internal surface to a concentric shape to an outside diameter in the attractive surface of the armature or a yoke and forming a fine air gap.

CONSTITUTION: A fine air gap in 0.1-1.5mm is shaped on the internal diameter side of an attractive surface 4 oppositely faced to a yoke 1 of an armature 5 attracted to the yoke 1, and an adhesive surface to the yoke 3 is formed to the outer circumference of the armature 5 to a ring shape. The outside diameters of both the yoke 1 and the armature 5 are shaped in 90mm in the attractive surfaces of the yoke 1 and the armature 5, a 50% NiFe alloy having high saturation magnetic flux density (Bs) and low coercive force (Hc) is used as a magnetic material employed, and the air gap having a 72mm diameter concentric to an outside diameter and width of 0.1mm-0.5mm is formed to an armature inside diameter section in the attractive surface 4. Accordingly, when the armature 5 attracted to the yoke 1 has a specified current value, required attractive force is held, and the title electromagnet is released in a short time when holding currents are released.