The present invention addresses the problem of implementing a pulley device with an embedded unidirectional clutch, with which the influence of auxiliary automobile machinery on a rotary shaft due to fluctuations in the rotation of the engine can be sufficiently reduced. A sleeve (1b) is configured from an inner-diameter-side sleeve (24) and an outer-diameter-side sleeve (25), a unidirectional clutch (3) is provided between the outer-diameter-side sleeve (25) and a pulley (2), and a coiled torsion spring (18a) capable of transmitting torque between the inner-diameter-side sleeve (24) and the outer-diameter-side sleeve (25) is provided between these members (24, 25). When the rotational speed of the pulley (2) becomes slower than the rotational speed of the outer-diameter-side sleeve (25), the inner-diameter-side sleeve (24) and the outer-diameter-side sleeve (25) rotate relative to one another due to the elastic force of the coiled torsion spring (18a), until the elastic force of the coiled torsion spring (18a) is released, after which the unidirectional clutch (3) becomes incapable of transmitting torque between the pulley (2) and the outer-diameter-side sleeve (25).