Abstract: A power transmission apparatus includes a sleeve assembly disposed rotatably around a stationary support shaft and having an annular surface unit that is formed with a plurality of axially extending slots. A plurality of rollers are confined respectively and rollably within the slots. A coiled torsional spring is disposed around the sleeve assembly, is spaced apart from the rollers, and is fastened to the driving gear at one end and to the driven gear at the other end. During rotation of a primary driving gear that is sleeved fixedly on the sleeve assembly, when a secondary driving gear rotates on the sleeve assembly, the spring is wound around the sleeve assembly so as to clamp the rollers between the spring and the sleeve assembly, thereby transmitting a torque from the primary driving gear to a driven gear on the support shaft.