A power transmission mechanism has a first rotating member rotating around an axis, a second rotating member rotating around the axis and an elastic member located between the first rotating member and the second rotating member. The first rotating member has a first rotating member surface, and the second rotating member has a second rotating member surface. The elastic member has at least a protrusion contacting at least the first rotating member surface. The protrusion extends in a circumferential direction of the first rotating member. The protrusion has gradually tapering shape toward the first rotating member surface. The elastic member is deformed by compression as the elastic member engages the first rotating member surface and the second rotating member surface by rotation of the first rotating member, thereby causing relative rotation of the first rotating member and the second rotating member.