PURPOSE: To provide an electromagnetic chuck which enables a machined work to be easily and quickly mounted/demounted on/from a machine tool, and does not restrict a range capable of being set for facing at the time of flatening.

CONSTITUTION: A stepped rectangular hole 12 composed of three recessed sections 12a through 12c each of which is different in dimension are provided for one surface of an electromagnetic chuck main body 11, magnetic poles 13a through 13c are provided in the vicinities of both the ends of the bottom sections of the recessed sections 12a through 12c respectively, four square holes distributed in the width direction are provided in the vicinities of both the ends of a carbon jig 14, the carbon jig 14 comprises a top 15 installed, which includes leg pieces 15a fixedly engaged with the square holes, and let adsorption force taking place groundlessly be taken care of by a magnetic force regulator.