NOVELTY - A hydrogen producing device comprises a reaction portion, and sets supply amount of each material by selecting one from two or more set of predetermined values corresponding to the required hydrogen production volumes. The supply amount of air, oxygen or oxidizing agent (1c) is varied and controlled such that the reaction portion has a preset temperature range.    USE - As internal source of hydrogen for fuel cell electric power generation system and distributed power source for households or buildings (both claimed) and for emergency use in disaster situations.    ADVANTAGE - The hydrogen producing device is inexpensive and compact and has improved hydrogen production accuracy. The device reduces waste and failure rate. Reflux of off-gas to hydrogen storage unit is prevented. The device maintains reaction temperature easily, quickly and securely by controlling the amount of air, oxygen or oxidizing agent to the reaction portion and controls load based on the temperature. Danger of improper control is prevented. The on/off valves and flow setting units are inexpensive and easy to control compared with control valves for flow control. Flow control is performed using a simple hardware. The hydrogen storage unit absorbs and reduces step-like variation and pulsation. Specific gases such as carbon monoxide in fuel cells which provides ill effects on power generation are removed. Faster control response against external disturbance is obtained and control which causes additional disturbance is prevented. The on/off valves detects aged deterioration of failure of the system. The power generation system is operated stably even in dusty environments by using a filter unit.    DETAILED DESCRIPTION - The hydrogen producing device comprises a reaction portion to which the device supplies at least one type of material together with air, oxygen or an oxidizing agent to produce hydrogen by a specific chemical reaction. The device sets supply amount of each material by selecting one from two or more set of predetermined values corresponding to the required hydrogen production volumes. The supply amount of air, oxygen or oxidizing agent is varied and controlled such that the temperature of the reaction portion is within a preset temperature range.    INDEPENDENT CLAIMS are included for:    (1) a fuel cell electric power generation system comprising a hydrogen producing device for generating electric power using the hydrogen produced by the hydrogen producing device as a raw material; and    (2) a distributed power source for home use or for buildings, which comprises hydrogen producing device and fuel cell. The fuel cell is implemented by a polymer electrolyte fuel cell.    DESCRIPTION OF DRAWING(S) - The figure shows a block diagram of a hydrogen producing device and a fuel cell power generation system.    methane (1a)    water (1b)    air, oxygen or oxidizing agent (1c)    flow setting units (2a,2b,3)