Abstract: A bicycle folding device comprising a first folding portion and a second folding portion. The first folding portion has a groove, a first axial hole, an axial arranged guide hole, a buckling groove. The second folding portion has an inner axial hole. The pivotal unit serves to pivot the first folding portion and the second folding portion. The quick-detaching unit serves to position the second folding portion. A lever set is placed at a middle section between the second inner end and the second outer end. The lever set has a lever, a handle at a front end of the lever; and a key which is supported by an elastomer and is at a distal end of the lever set. By above structure, the bicycle frame can be assembled and detached easily and firmly. No noise occurs as the bicycle frame is transferred.