To miniaturize the whole system and to improve energy efficiency by adopting a reforming reaction, in which endothermic reaction and exothermic reaction are made to coexist, to dispense with or miniaturize equipment such as a heating device and using a liquid except a gas such as air as an oxidizing agent.

In a fuel reforming device 12, methanol, water and hydrogen peroxide are used as raw materials for reforming reaction. A methanol aqueous solution and a hydrogen peroxide aqueous solution are housed respectively in fuel tanks 21 and 22 as fuel raw materials. A controller 27 controls the drive of pumps 28 and 29 based on the detected value of a temperature sensor 32 and the feed ratio of the fuel raw materials (that is the fuel composition) fed to a reformer 24 through an evaporator 23. In the reformer 24, methanol steam reforming reaction (endothermic reaction) and methanol hydrogen peroxide reforming reaction (exothermic reaction) are made to coexist to adopt an autothermal system for controlling the fuel composition to balance the income and outgo of heat of reaction.