To ensure the temperature control of roller surface by applying to an induction heating coil a magnetic guide member guiding flux generated by the induction heating coil to a secondary conductor.

A magnetic guide 15' is structured to have a plurality of convex magnetic poles extending radially outwardly to provide uniform temperature on the roller surface. A direct current coil is provided radially inside the convex pole, to detect jule loss generated by the convex pole by a temperature sensor mounted on the roller surface to instruct direct current control instructions from a controller to a plurality of coils located axially at both ends to control the direct current to provide homogenous temperature at the roller surface. The entire coil comprising the direct current coils located axially at both ends and the alternative current coil therebetween is instructed by the controller with alternative current instructions, a plurality of coils located axially at both ends are provided with control instructions for both direct and alternative current, the interposed coil is provided only with the alternative current instructions.