PURPOSE: To obviate a separate type fan and execute cooling action without enlarging the diameter of a cylindrical drum by providing a driving drum composed of the cylindrical drum made of a magnetic substance or the like with a fin cooling structure.

CONSTITUTION: A cooling fan 4 formed of small plate-shaped pieces 4a, 4b is a fixed to the inside of a cylindrical drum 10-1 on both the sides of a rib 10-3. When a circular arc-shaped linear motor 11 is energized, an eddy current flows in a driving drum 10, and Joule-heat is thereby generated to rise the temperature of the driving drum 10. On the other hand, the driving drum 10 rotates, and an cooling wind is therefore generated by the centrifugal force of the cooling fin 4 for cooling the cooling fin 4.