A shaft member holding mechanism comprising: a shaft member arranged rotatably about a rotation axis; a bearing that supports the shaft member rotatably, including an outer ring portion, and an inner ring portion that holds the shaft member and is arranged at an inside of the outer ring portion so that the inner ring portion can rotate relatively to the outer ring portion; a holding member having a bearing holding portion that holds the outer ring portion of the bearing in a state where a rotation of the outer ring portion is regulated; and an inclination suppression member that is arranged at one side of the bearing in the rotation axis direction of the bearing and suppresses the bearing from inclining.