PURPOSE: To shorten the time required for starting a reformer by flowing nitrogen to a process part of a reforming device in the direction opposite to that in reforming operation at the time of raising temperature in starting and enabling a temperature rise of a raw material gas inlet part in a short time.

CONSTITUTION: The aforementioned reformer for a fuel cell is formed from a burning part 3 for a reforming device, a process part 4 of the reforming device, the reforming device, etc. A fuel composed of hydrocarbons is converted into hydrogen and fed to the fuel cell. Nitrogen heated at a high temperature is made to flow to the above-mentioned process part 4 at the time of raising the temperature in starting the aforementioned reformer in the direction opposite to the gas flow in reforming operation to heat the raw material gas inlet side of a catalyst in the reforming device in a short time.