Abstract: Fuel cell apparatus and method for feeding a fuel for fuel cell. Optimal power generation for the output demanded by a fuel cell can be achieved. A fuel mixer can adjust the methanol concentration of a mixed solution, and it adjusts the concentration of the mixed solution to an optimal methanol concentration for a load. Information on the methanol concentration detected by a concentration sensor is sent to a controller and referred to when the fuel mixer adjusts the methanol concentration of the mixed solution. The concentration sensor 115 provided immediately before the fuel cell can achieve power generation while detecting the substantial methanol concentration of the mixed solution fed to the fuel cell.