NOVELTY - A fuel cell system (100) comprises hydrogen generating apparatus (1) which has modification part (14) where raw material and water are supplied and which produces hydrogen-containing gas by reforming reaction, selective oxidation part (17) where selective oxidation air is supplied and which reduces carbon monoxide concentration in hydrogen-containing gas produced by modification part by selective oxidation reaction, and selective oxidation temperature detection part (20) which detects temperature of selective oxidation part, and fuel cell (2).    USE - A fuel cell system for solar energy power generation system and storage battery.    ADVANTAGE - Carbon monoxide concentration of hydrogen-containing gas supplied to fuel cell can be reduced, and carbon monoxide poisoning and service life decline of fuel cell can be prevented.    DETAILED DESCRIPTION - A fuel cell system (100) comprises hydrogen generating apparatus (1) which has modification part (14) where raw material and water are supplied and which produces hydrogen-containing gas by reforming reaction, selective oxidation part (17) where selective oxidation air is supplied and which reduces carbon monoxide concentration in hydrogen-containing gas produced by modification part by selective oxidation reaction, and selective oxidation temperature detection part (20) which detects temperature of selective oxidation part, fuel cell (2) where hydrogen-containing gas and oxygen-containing gas are supplied and electric power is generated, control part (12) which sets upper limit W of electric power generation output of fuel cell, and storage part which stores actual electric power generation output Wr of fuel cell during instruction process to fuel cell so that control part may output with rated electric power generation output value Wmax. Value which pulls actual electric power generation output Wr from rated electric power generation output Wmax is set as difference delta W. When temperature of selective oxidation part is below threshold value T, upper limit W of electric power generation output is set to Wmax. When temperature of selective oxidation part exceeds threshold value T, upper limit W of electric power generation output is set to W2 which is obtained by subtracting delta W from W1.    DESCRIPTION OF DRAWING(S) - The drawing shows a block diagram of the fuel cell system. (Drawing includes non-English language text).    Hydrogen generating apparatus (1)    Fuel cell (2)    Control part (12)    Modification part (14)    Selective oxidation part (17)    Selective oxidation temperature detection part (20)    Fuel cell system (100)