PURPOSE: A fuel reformer burner of a fuel cell system is provided to combust fuel gas and anode off gas and to prevent backfire in burning anode off gas. CONSTITUTION: A fuel reformer burner(300) comprises: a fuel supply parte(320) to which fuel is supplied; an anode off gas supply part(310) to which anode off gas is supplied from a fuel batter stack; and a combustion air supply part(330) to which combustion air is supplied. The combustion air supply part is formed longer to the discharge direction of the fuel than the fuel supply part and anode off gas supply part.
