Conventional electromagnetic devices have a movable core passing through the interior of a coil bobbin around which a coil is wound. Because the coil bobbin and the movable core are movable, the movement of the movable core causes the coil bobbin to be worn away. Movable wear debris that is generated from the coil bobbin increases as the coil bobbin is worn away, thereby increasing friction of the movable core when it moves. This causes the movement of the movable core to be unstable, which results in a reduced life of the electromagnetic device. Consequently, a coating made from a rigid polyvinyl chloride resin is applied to the movable core or the movable core is provided with an irregular surface to make recessed portions serve as oil reservoirs, thereby improving movability and ensuring the life of the device. The electromagnetic device as described above, in which the coil bobbin and the movable core are movable, is disclosed as a conventional technology.