PURPOSE: To balance the temperature distribution of a hollow roll in its axial direction by causing the end portion of an iron core to protrude from the end portion of a solenoid coil and extend into the hollow portion of an end shaft, and forming a closed magnetic circuit of the iron core, the end shaft, the hollow roll, the end shaft and the iron core.

CONSTITUTION: When an electromagnetic coil 6 is excited by AC power a magnetic flux induced thereby forms a closed magnetic circuit of an iron core 8, the inside face portion 7a of an end shaft 7, the inner peripheral portion 1b of a hollow roll 1, the inside face portion 7a of the end shaft 7 and the iron core 8, and an electromotive force is induced in the inner peripheral portion 1b of the hollow roll 1 and the inside face portion 7a of the end shaft 7, and an eddy current flows through the inner peripheral portion 1b of the hollow roll 1 and the inside face portion 7a of the end shaft 7 so that the hollow roll 1 and the inside face portion 7a of the end shaft 7 are heated. In this way, the inside face portion 7a of the end shaft 7 is heated so that heat captured from the hollow roll 1 by the inside face portion 7a of the end shaft 7 is remarkably decreased to balance the temperature distribution of the hollow roll 1 in its axial direction to thereby uniformly heat paper or film, etc.