NOVELTY - A fuel cell system has fuel gas supply start command unit, operational status detector, deterioration preventing control unit, and fuel gas feed rate control unit. Control for preventing deterioration of fuel cell is performed at start-up of the fuel cell system.    USE - Used as electrochemical device for converting chemical energy to electric energy.    ADVANTAGE - Prevents deterioration of catalyst and catalyst carried at start-up and shutdown of the fuel cell system.    DETAILED DESCRIPTION - The fuel cell system comprises fuel gas supply start command unit for commanding start of fuel gas supply to fuel cell of the system; operational status detector for detecting operational status of the fuel cell; deterioration preventing control unit for performing control for preventing deterioration of the fuel cell based on output of the detector and output of the fuel gas supply start command unit; and fuel gas feed rate control unit for controlling fuel gas feed rate according to the output of the fuel gas supply command unit and the control of the deterioration preventing control unit. Control for preventing deterioration of fuel cell is performed at start-up of the fuel cell system. The fuel gas supply is started according to the output of the fuel gas supply start command unit, and after the control for preventing deterioration of the fuel cell is started. The fuel gas feed rate is increased by the fuel gas feed rate control unit. An INDEPENDENT CLAIM is also included for a method for starting up the fuel cell system comprising supplying fuel gas to fuel cell; detecting operational status of the fuel cell; performing control for preventing deterioration of the fuel cell based on the detected operational status after starting the supply of fuel gas; and increasing feed rate of fuel to be supplied to the fuel cell after starting the control for preventing deterioration of the fuel cell.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view illustrating reactions in the fuel cell at start-up/shutdown.