PURPOSE: To restrain generation of foreign matter and to reduce irregularities and cracks on a belt surface by treating a surface of a spring belt by electrolytic polishing.

CONSTITUTION: A spring belt 1 is in a state of an extension coil spring which is always provided with tension, and is in contact with a groove 3 of a pulley 2 by tension of itself. A surface of the spring belt 1 is treated by electrolytic polishing for mirror surface treatment to remove a projecting part on a surface which is subjected to a load concentrically and cut off and cracks wherein foreign matters are easy to gather. Thereby, the surface is made as smooth as possible. Furthermore, a V-shaped cross section of the groove 3 of the pulley 2 enables reduction of a contact area between the spring belt 1 and the groove 3, and reduction of a play amount of a belt. Thereby, the spring belt 1 can always acquire a stable contact part 4 by its tension and prevents center deviation and removal of a belt caused by revolution. According to said interaction, mutual sliding of smooth surfaces can be realized, thereby enabling smooth sliding of the spring belt 1 and reduction of a dust amount.