PURPOSE:To suppress the temperature rise of a coil by forming plural groove parts in the main magnetic pole and auxiliary magnetic pole of an electro-magnetic coil. CONSTITUTION:A coil 2 is provided in a main magnetic pole 1 for the electro- magnetic coil and auxiliary magnetic poles 3a and 3b are arranged in the outside of the coil 2. Then, an E-shaped core is formed by the main magnetic pole 1 and auxiliary magnetic poles 3a and 3b. Grooves are provided in the auxiliary magnetic poles 3a and 3b. Thus, since the surface area of an electromagnetic coil core part can be enlarged, the radiation of heat is promoted. Then, since the temperature rise of the coil can be suppressed, the lowering of intensity for a generating magnetic field, which is caused by the temperature rise, the insulation destruction of the coil or the generation of damage in the coil itself can be effectively prevented.
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