SOLID ELECTROLYTE FUEL CELL

A solid oxide fuel cell capable of maintaining performance over a long time period by appropriately changing fuel cell module operating conditions. The present invention is a solid oxide fuel cell (1), having a fuel cell module (2), a fuel supply device (38), an oxidant gas supply device (45), and a controller (110) for controlling the amount of fuel supplied from the fuel supply device; the controller is furnished with a degradation determining circuit (110a) for determining degradation in the fuel cell module and a degradation response circuit (110b) for changing fuel cell module operating conditions based on the degradation determination by the degradation determining circuit; the degradation determination stores fuel cell module operating results arising from the operating conditions changed by the degradation response circuit, and executes further degradation determination based on the stored operating results.