Abstract: A pulley device formed by molding resin effectively eliminates the destruction of the main body of the pulley device by an impact from the outside, such as collision with flying foreign matter, and reduces manufacturing cost. The pulley body 6 is formed to have the high-impact strength so that the thickness of a flange portion of the pulley at the side opposite the side of a rotary machine is larger than the thickness of a flange portion at the side of the rotary machine. In consideration that foreign matter flying from the outside tend to hit and break portions of the main body 6 of the pulley device at the side opposite the side of the rotary machine whereby cracks and breakage take place in that portion, the thickness of the flange portion of the main body of the pulley device at the side opposite the rotary machine is increased to thereby improve the impact strength.