NOVELTY - The hydrogen generator has a raw-material supplier (1), a water supplier (3), a modifier (4), an oxidizing-agent supplier (9), a purifier (11), a device (13a,13b) for adjusting temperature of the purifier, and a controller (14). The controller controls the raw-material supplier during shutdown operation. The adjusting device is controlled and the temperature of the purifier is maintained at a temperature higher than the temperature during normal operation.    USE - For fuel cell systems (claimed) used for electric-power generation.    ADVANTAGE - The hydrogen generator rapidly recovers the activity of selective-oxidation catalyst, reliably and stably decreasing the carbon monoxide in hydrogen-rich gas. Catalyst poisoning is also prevented.    DETAILED DESCRIPTION - The hydrogen generator has a raw-material supplier (1), a water supplier (3), a modifier (4), an oxidizing-agent supplier (9), a purifier (11), a device (13a,13b) for adjusting temperature of the purifier, and a controller (14). The modifier reforms the raw material and water, and generates hydrogen-rich gas. The purifier has a selective-oxidation catalyst which decreases carbon monoxide in the hydrogen-rich gas by selective oxidation using the supplied oxidizing agent. The adjusting device controls the temperature of the purifier. The controller controls the raw-material supplier during shutdown operation. The flow path through which hydrogen-rich gas flows is purged with the raw material during starting operation and high-temperature operating period. The adjusting device is controlled and the temperature of the purifier is maintained at a temperature higher than the temperature during normal operation. An INDEPENDENT CLAIM is included for fuel cell system.    DESCRIPTION OF DRAWING(S) - The figure shows the block diagram of the hydrogen generator. (Drawing includes non-English language text)    Raw-material supplier (1)    Water supplier (3)    Modifier (4)    Oxidizing-agent supplier (9)    Purifier (11)    Temperature adjusting devices (13a,13b)    Controller (14)