To reduce the weight of the whole flywheel and to improve the wear resistance on a clutch facing surface by using a material having a relatively small specific gravity such as aluminum composite material for the inside part of the flywheel, and using a material having a relatively large specific gravity such as cast iron for the circumferential part thereof.

In this flywheel 1, a disc-like inside part 4 having a mounting part 2 on a crank shaft and a clutch facing surface 3 is formed of a composite material using aluminum or aluminum alloy having a relatively small specific gravity as the base material, or aluminum MMC. On the other hand, an L- shaped sectional ring-like circumferential part 5 fitted to the circumference of the inside part 4 is formed of a metallic material having a large specific gravity, particularly, an iron material such as cast iron. According to this, a lighter weight can be attained while ensuring the inertial mass required for the flywheel 1. The composite material such as aluminum MMC in the inside part 4 and the iron metallic material such as cast iron in the circumferential part 5 may be fastened together by use of a plurality of bolts 7.