The present invention provides a chain alignment mechanism of a transmission for a bicycle which includes a drive sprocket wheel which is rotatably driven by a crankshaft, a driven sprocket wheel which is drivably connected with an output shaft which is rotated in an interlocking manner with a drive wheel of the bicycle, and an endless chain which is wound around the above-mentioned drive sprocket wheel and the above-mentioned driven sprocket wheel, wherein even when the chain of the transmission for the bicycle is deflected or slackened due to a driving manipulation of the bicycle, the vertical vibration of the bicycle or the like, the chain is reeled in the drive sprocket wheel in a row in an aligning manner. A chain guide member is arranged on an endless-chain-reel-in side of the above-mentioned drive sprocket wheel.