Abstract: A torsional damper type flywheel device including a drive side flywheel, a driven side flywheel rotatable relative to the drive side flywheel, at least one kind of spring mechanism connected between the drive side and driven side flywheels, and a friction mechanism arranged in series with the spring mechanism. An inertial plate is fastened to the drive side flywheel so as to construct one portion of the drive side flywheel so that a mass center of the drive side flywheel is shifted to an engine side to prevent the drive side flywheel from being deformed to an engine side when rotated at high speeds. Further, the engine side drive plate is bent at its radially intermediate portion so that a radially outer portion of the drive plate approaches the axial center of the drive side flywheel. As a result, an axial increase in width of the flywheel device due to the provision of the inertial plate is minimized.