NOVELTY - The fuel cell power generating device has hydrogen generation apparatus (120) for producing hydrogen rich gas, fuel cell (107), hydrogen rich gas flow path (110) provided between hydrogen production apparatus and fuel cell, and off gas flow path (111). The apparatus has an air supply portion (105), a modification portion (103), carbon monoxide decreasing portion (106), and a combustion portion (104). The air supply portion has a control portion (114) for controlling amount of air supplied to combustion portion.    USE - As fuel cell power generating device.    ADVANTAGE - The fuel cell power generating device prevents incomplete combustion and suppresses carbon monoxide concentration in combustion exhaust gas during electric power generation.    DETAILED DESCRIPTION - The fuel cell power generating device has hydrogen generation apparatus (120) for producing hydrogen rich gas, fuel cell (107), hydrogen rich gas flow path (110) provided between hydrogen production apparatus and fuel cell, and off gas flow path (111). The apparatus has an air supply portion (105), a modification portion (103), carbon monoxide decreasing portion (106), and a combustion portion (104). The air supply portion supplies air to modification portion. The modification portion carries out reaction of raw material and water vapor, and produces reformed gas. The carbon monoxide decreasing portion reduces concentration of carbon monoxide in reformed gas. The combustion portion burns gas and heats modification portion. The fuel cell generates electric power using oxidizing agent gas and hydrogen rich gas. The hydrogen rich gas flow path circulates hydrogen rich gas. The flow path (111) is provided between fuel cell and combustion portion, and supplies off gas not required for electric power generation. The air supply portion has a control portion (114) for controlling amount of air supplied to combustion portion. The control portion controls air supply portion, such that electric power generation starts after predetermined period and excess air ratio is higher than excess air ratio with respect to time of electric power generation.    INDEPENDENT CLAIMS are included for the following:    (1) operation of fuel cell power generating device;    (2) program; and    (3) recording medium.    DESCRIPTION OF DRAWING(S) - The figure shows the block diagram of fuel cell power generating device. (Drawing includes non-English language text)    Raw material supply portion (101)    Water supply portion (102)    Modification portion (103)    Combustion portion (104)    Air supply portion (105)    Carbon monoxide decreasing portion (106)    Fuel cell (107)    Hydrogen rich gas flow path (110)    Off gas flow path (111)    Control portion (114)    Hydrogen generation apparatus (120)