Fuel cell system and fuel cell starting method

A method of starting a fuel cell system which includes:

• a power generation cell having an electrolyte sandwiched between a positive electrode and a negative electrode,
• a first storage vessel for storing a low-concentration fuel having a predetermined concentration, and
• a second storage vessel for containing a high-concentration fuel higher in concentration than said low-concentration fuel,
• with said fuels differing in concentration and stored in said first storage vessel and said second storage vessel being switchedly supplied according to a temperature of said power generation cell, said method comprising the steps of:
• supplying said fuels to said negative electrode while setting a first quantity of said high-concentration fuel supplied to said negative electrode to be smaller than a second quantity of said low-concentration fuel supplied to said negative electrode;
• and
• supplying an oxidizer to said positive electrode in a third quantity set to be smaller than a fourth quantity of said oxidizer supplied to said positive electrode in the case where the temperature of said power generation cell is at or above a predetermined temperature.