PURPOSE: To obtain the technically finished number of strong points such as the safety and the safe traveling of a bicycle at present, stable straight advance performance, and the compactness as the strong point of bicycle having different diameter wheels which existed in the past.

CONSTITUTION: As for a bicycle 1 having different diameter wheels is constituted of a large diameter front wheel 2 and a small diameter rear wheel 3, and is equipped with a driving part having a pedal 6 and a crank 7 for driving the driving shaft of the hub of the front wheel 2, at the top edge part of a front fork 5 which is continuously installed on a handle 4, and the driving shaft for the hub of the front wheel 2 is supported in the rear part by a prescribed quantity from the vicinity of the top edge of the front fork 5. Further, a planetary gear device 8 having a ratchet device between a driving part having the pedal 6 and the crank 7 and the driving part for the hub of the front wheel 2 is installed.