Abstract: A reversible drive device for bicycles, allowing a bicycle to go forward by a normal or reversed rotating force of a pedal without forcing a user to operate any lever, is disclosed. The drive device has a simple construction with a reduced number of parts and allows the rear wheel 10 to be rotatable in a reversed direction, thus allowing the bicycle to be moved backward. The drive device is integrated into a single assembly and is detachably attached to either the rear wheel hub shaft 11 or a pedal shaft 21, so the device allows a user to easily repair or change the drive device and improves work efficiency while producing the drive device. Two crescent stoppers 18 are formed on each end of the fixed shaft 17 so as to effectively prevent the shaft holding yoke of the rear wheel fork 1 from being unexpectedly opened.