To provide a fuel cell device capable of extending the years of service life of a reformer by suppressing thermal runaways. The present invention is a solid oxide fuel cell device (1), including a fuel cell module (2) having fuel cell units (16); a reformer (20b) disposed above the fuel cell units, for producing hydrogen by a partial oxidation reforming reaction and a steam reforming reaction; a vaporizing chamber (20a) disposed adjacent to the reformer; a combustion chamber (18) for heating the vaporization chamber; a water supply device; an electrical generation oxidant gas supply device; and a controller (110) for raising the fuel cell units to a temperature at which electrical generation is possible; whereby over the entire period of the startup step, the reforming oxidant gas supply device and water supply device are controlled so that partial oxidation reforming reactions do not occur independently in the reformer.