To substantially shorten a start time, to cope with fluctuations in load current even if the reformer is operated under a normal condition by always supplying a fixed amount of methanol and water to the reformer, and to utilize hydrogen in reformed gas.

This on-vehicle fuel cell system has a hydrogen storage means, occludes hydrogen, which is exhausted from a fuel cell stack 11 and is not used in a fuel cell stack 11, by using the hydrogen storage means, and discharges the hydrogen stored in the hydrogen storage means as required, in order to supply it to the fuel cell stack 11. This on-vehicle fuel cell system is also provided with a means, which has at least two or more hydrogen storage means 14, 15, occludes the hydrogen by using at least one of the hydrogen storage means, and discharges the hydrogen by using at least the other hydrogen storage means, in order to alternate a roll to absorb the hydrogen and a roll to discharge the hydrogen one by one.