The problem addressed by the present invention is to provide a structure that enables the extremely simple mounting of a clutch means for linking a plurality of single-passenger bicycles in a single continuous line to convert the bicycles into a multi-passenger bicycle, and facilitates the manufacture of a mutually linkable bicycle. A clutch means includes an immobile tube (60) disposed between a top tube (2) and a head tube (6) of a bicycle frame, with a bearing portion (20) mounted to one of the facing end portions and axially supporting the end portions, whereby the top tube (2) and the immobile tube (60) are disposed so as to be capable of relative rotation. In the outer periphery of the bearing portion (20) and the immobile tube (60) axially supported therein, pin holes (22, 62) are respectively opened. The pin holes (22, 62) are bored at positions that are centrally aligned when a front fork (4) of the bicycle is are linearly positioned. By inserting or removing a fixing pin (8) into or from the two pin holes (22, 62) when aligned, the top tube (2) and the immobile tube (60) can be converted so as to be capable or incapable of relative rotation.