To provide a fuel cell device capable of preventing an auxiliary machine housed in an outer case from being frozen.

The fuel cell device is divided into a module housing chamber 26 where a fuel cell module 25 is housed and an auxiliary machine 27 where the auxiliary machine is housed by a partition member 24 provided in the outer case 23. The device is provided with: a module housing chamber suction and exhaust openings 35 for sucking and exhausting air in the module housing chamber 26 at a part of the outer case 23 comprising the module housing chamber 26; an auxiliary machine housing chamber suction and exhaust opening 36 for sucking and exhausting air in the auxiliary machine 27 at a part of the outer case 23 comprising the auxiliary machine 27; and a controller 40 for controlling a ventilation means 37 to circulate air of one of the module housing chamber 26 and the auxiliary machine 27 to the other on the basis of the outer air temperature. Consequently, the freezing of the auxiliary machine can be efficiently suppressed.