Power transmission system

A power transmission apparatus comprising

• a pulley rotationally attached to a casing and
• a hub, which is located at a front end of a shaft, wherein the shaft projects from the casing, the hub rotates integrally with the shaft, the hub transmits power from the pulley to the shaft, and the hub includes
• an inner hub fastened to the shaft,
• an outer ring, which is located radially outward of the inner hub and at an outer peripheral part of the hub and, and
• a torque transmission elastic member, which is integrally molded together with the inner hub and the outer ring, is solid, and fills a space between the inner hub and the outer ring, and
• a gate mark, which is a protrusion and is a mark of a remainder of an injection gate used in the integral molding, wherein the gate mark is located on the torque transmission elastic member, is made of the same material as the transmission elastic member, is formed on a line extending from a metal surface that forms a front end of the outer ring, and protrudes generally in an axial direction away from the outer ring.