PURPOSE: To miniaturize a motor core to reduce the cost of an apparatus by fitting the bridge outer peripheral part of a stator core slidably with a tapered plate magnetic material.

CONSTITUTION: On a base stand 212 fixed at a stator core 201, a tapered plate magnetic material 214 fixed at the tip of an adjusting screw 213 is detent-held at the bridge outer peripheral part 215 of said stator core 201 by the use of said adjusting screw 213. Said plate magnetic material 214 slides along the bridge outer peripheral part 215 by rotation of the adjusting screw 213 to increase and decrease the effective magnetic path width A of a bridge part. That is, said adjusting screw 213 is rotated to slide the plate magnetic material 214 and to increase and decrease the effective magnetic path width of said bridge part of the stator core 201 so that a motor speed can be regulated and moreover in a stepless manner. Thus, the speed of a shading-coil motor can be regulated without requiring a governor coil.