In a power transmission utilizing a bushingless roller chain, the inner links of the chain have chain guide-contacting backs that have a convex arcuate shape, and the outer links are shaped so that they do not contact the chain guides. The rollers are wider than the sprocket teeth that they engage, and widthwise gaps between the ends of the rollers and the outer link plates allow the inner link plates to move in the widthwise direction. The gap between the inner surfaces of the rollers and the outer surfaces of the connecting pins of the chain is larger than the gap between the inner surfaces of the holes in the inner link plates and the outer surfaces of the connecting pins that extend through them.