To produce less wear in an input shaft of a transmission by reducing the relative rotation of a bearing and the input shaft of the transmission.

The supporting structure for the input shaft 5 of the transmission to be supported with its end fitted into the bearing 4 fitted and fixed to a flywheel 3 and having an inner race 4a and an outer race 4b relatively rotatable with clearance fit comprises a seal ring 10 provided in a compressed condition between the inner race 4a and the input shaft 5 of the transmission. Thus, the input shaft 5 of the transmission and the inner race 4a are relatively rotated to reduce the relative rotation of the input shaft 5 of the transmission and the bearing 4, thereby producing the less wear in the input shaft 5 of the transmission.