To reduce noise as well as to improve durability by bringing the chain side support surface into plane contact with the idler side support surface, by arranging the chain side support surface on the rotational directional outside of link plates, and forming this chain side support surface in a curved shape recessed inside in the rotational direction.

In a silent chain 50, the chain side support surface 76 is arranged on the rotational directional outside of link plates 64 and 72. This chain side support surface 76 is arranged by being formed in a curved shape of a radius of curvature R1 recessed toward the rotational directional inside belly surface. Therefore, a motive power transmission device can support the rotational directional outside chain side support surface 76 of the link plates 64 and 72 of the silent chain 50 along an idler 48. In this motive power transmission device, abrasion resistance can be improved by plane contact, vibration/noise can be reduced, a chain layout can be easily changed to the silent chain, and a cost can be reduced.