Disclosed are a reformer with a plurality of heaters for precisely controlling the temperature thereof, and a fuel cell system using the same. The fuel cell system is constructed with an electric generator that generates electricity through electrochemical reaction between hydrogen and oxygen, a pump that supply the electric generator with oxygen in the air, a reformer that supplies the electric generator with hydrogen, a water container that supplies the reformer with water, and a fuel container that supplies the reformer with reforming fuel containing hydrogen and inflammable combustion fuel. The reformer in the fuel cell system is constructed with a reforming reaction unit that receives thermal energy and reforms reforming fuel containing hydrogen into hydrogen through a catalyst, a heat source unit that supplies the reforming reaction unit with heat obtained by burning inflammable combustion fuel, and an auxiliary heat source unit that supplies the reforming reaction unit with heat generated from a hot wire using electric energy.