A reformer for a solid state polymer electrolyte fuel cell includes a burner 1 forming a flame, a reforming portion 2 surrounding the burner and having an exhaust port 22 and exhausting a reformed gas from the exhaust port 22; and a heat exchanger 4 having a higher temperature side, the higher temperature side being connected directly with the exhaust port 22 of the reforming portion 2, the heat exchanger 4 establishing heat exchange between the reformed gas and a raw material gas.