PURPOSE: To facilitate assembling and disassembling work of flywheel device by making it in such a manner as a generator rotor, spider and a thrust collar may be drawn out together in an integrated body, while leaving behind on a pit, the flywheel fitted along an outer diameter section of the cylinderlike spider.

CONSTITUTION: A flywheel 22 is composed, by fitting along an outside diameter section of a cylinderlike spider 21 the plural number of discs 23 provided with a central hole 23a each. The weight of the flywheel 22 is supported from below by the plural number of supporting pins 24 inserted into the lower part of the spider 21 in the radial direction. By supporting the lower end of the flywheel 22 with a jack and subsequently drawing out supporting pins 24, a generator rotor 2, the spider 21 and a thrust collar 25 maq be lifted off the flywheel 22, as an integral unit, while leaving the flywheel 22 on a base pit.