Optimized heating of a reformer in a fuel cell apparatus

A fuel cell apparatus includes a reformer (100) including a bottom wall (101), a top wall (102) facing the bottom wall (101), and a side wall (103, 104) connecting the bottom wall (101) and the top wall (102), a stack (200) generating electricity, a combusting portion (300) forming a bottom heating space (301), a side heating space (303, 304), and a top heating space (305), and a first guiding portion (900, 904) arranged above the reformer (100) and facing the top wall (102) of the reformer (100). The first guiding portion (900, 904) guides the combustible gas or the combustion exhaust gas guided from the side heating space (303, 304) to the top heating space (305) toward the top wall (102) of the reformer (100) to increase efficiency of the combustible gas or the combustion exhaust gas making contact with the top wall (102).