To prevent occurrence of overload due to locking of a rotation shaft 2 by imparting a torque limiter function to this power transmission device.

This device has a pulley 4 rotated by drive force of an engine, a hub 5 fixed on the rotation shaft 2, a cup member 8 connected with the pulley 4 via an elastic body 13 made of a rubber elastic material, a plate 7 interposed between the cup member 8 and the hub 5, a torsion spring 9 for connecting the cup member 8 and the plate 7, a steel sphere 14 engaged with both an engagement recess 5f formed on the hub 5 and an engagement hole 7b formed on the plate 7, and an escape recess 8f formed on the cup member 8. When a torque exceeding a set value acts, the cup member 8 and the plate 7 relatively rotate against elasticity of the torsion spring 9, and thereby the engagement hole 7b and the escape recess 8f are polymerized, the steel sphere 14 is pushed out to the escape recess 8f, engagement between the plate 7 and the hub 5 is released, and the torque is cut off.