A roller supporting device comprises a pair of supporting arms, a supporting shaft attached between the pair of supporting arms in a non-rotatable manner, and a roller having an inner hole in the central part thereof, the roller being disposed between the pair of supporting arms and being supported in a rotatable manner by the supporting shaft inserted through the inner hole, the roller being arranged to rotate along with the relative movement with a mating member by making the roller contact with the mating member, wherein a cut out portion, which extends in the axial direction on the outer circumferential surface of the supporting shaft, is formed at an appropriate portion except the portion on which the inner circumferential surface of the inner hole of the roller is pressed due to the load applied to the roller from the mating member, thereby defining an oil passage which extends in the axial direction between the supporting shaft and the inner circumferential surface of the inner hole of the roller.