To provide a direct methanol fuel cell device and an operation method of such intended to achieve enough anti-freeze characteristics and improved cold start-up operation.

The fuel cell device is provided with an anode space 2 and a cathode space 3 separated by a proton conductive film 4. A cathode supply line 8 is used for supplying oxygen-containing gas, and an anode line 5 is used for supplying an operation medium to the anode space and exhausting it. A representative temperature is measured with a sensor 11, as a function of which, the amount of an operation medium, such as methanol, to be supplied to the cathode space is controlled by a supply device 18, calculated with a control unit 17. Rise in concentration of the operation medium leads to lowering of freezing point, and, at time of starting of the device, to exothermic catalysis.