To provide a sprocket of a chain mechanism enabled in the reduction of its weight, material cost and manufacturing cost by preventing the insufficiency of rigidity depending on a place, and avoiding the waste of the material in a place in which the rigidity is sufficient.

The sprocket of the chain mechanism comprises a plurality of divided arc-shaped members 42 which are combined in the circumferential direction and formed into the annular sprocket as a whole, and each divided arc-shaped member 42 has: an inside arc-shaped member 52 arranged inside the radial direction of the sprocket 40; an outside arc-shaped member 50 arranged outside the radial direction of the sprocket 40; two end-connecting plates 54, 56 which are connected to ends of the inside and outside arc-shaped members 52, 50 in arc-shaped directions at their ends, and formed so as to elongate in the radial direction of the sprocket 40; and width-direction center plates 58 whose peripheries are joined to width-direction centers of the inside and outside arc-shaped members 52, 50 and width-direction centers of end connecting plates 54, 56.