PURPOSE: To correct the mounting position of a lever stopper so as to prevent a humming sound by allowing the projecting portion of a lever stopper for supporting a pin serving as the point of support of a lever to be received at the peripheral face of a rectangular hole provided in a brake stand.

CONSTITUTION: To assemble a lever stopper 12 into a brake stand 17, the projecting portion 19, 19' of the lever holder 12 is inserted into the rectangular hole portion 20 of the brake stand 17 and a mounting hole 21, 21' is adjusted to a screw hole 22, 22' and a mounting screw is tightened. The dimension (d) from the center of the mounting hole 21, 21' to the projecting portion 19, 19' is equal to that from the center of the mounting hole 22, 22' to the lower surface of the rectangular hole 20 and the length (a) of the rectangular hole 20 is greater than the outside width (b) of the lever stopper 12 by a minimum amount up to which the stopper 12 can be fitted into the hole. The lever stopper 12 is thus prevented from being installed obliquely even if carelessly assembled, so as to prevent an electromagnet from humming and to enhance the maneuverability of the device during assembly.