NOVELTY - The system (10) has a sub-zero countermeasure scavenging device executing sub-zero countermeasure scavenging to supply scavenging gas i.e. air, by a compressor with a greater flow volume than the scavenging gas supplied during deterioration countermeasure scavenging. The countermeasure scavenging device discharges generated water in an inner side of a fuel cell (11) when the temperature of the inner side of the fuel cell detected by a temperature sensor (41) drops to or below a predetermined temperature after stopping of the operation of the fuel cell.    USE - Solid polymeric membrane type fuel cell system for generating electric power by an electrochemical reaction with a fuel gas such as hydrogen gas and an oxidant gas such as air, in a vehicle.    ADVANTAGE - The sub-zero countermeasure scavenging is executed prior to the deterioration countermeasure scavenging, so that the generated water is discharged and the accumulated gas in the fuel cell is replaced with scavenging gas, thus eliminating the need to execute deterioration countermeasure scavenging, and hence reducing the energy necessary for deterioration countermeasure scavenging. The system eliminates the need to execute sub -zero countermeasure scavenging if the temperature of the fuel cell does not drop to or below freezing point after deterioration countermeasure scavenging is executed, thus enabling replacement of the accumulated gas in the fuel cell with scavenging gas and suppressing deterioration of the fuel cell, and hence reducing the energy necessary for sub-zero countermeasure scavenging. The discharge of the generated water accumulated in the fuel cell when the temperature of the fuel cell drops to or below freezing point after deterioration countermeasure scavenging is executed, prevents the generated water from freezing, thus ensuring the startability and power generation performance of the fuel cell, while preventing the damage of the fuel cell. The detection of the temperature of the inside of the fuel cell in the temperature detection step is stopped after the sub-zero countermeasure scavenging step, as no generated water is left in the fuel cell after sub-zero countermeasure scavenging, thus eliminating the need to monitor the temperature of the fuel cell, and hence reducing the energy necessary to detect the temperature of the fuel cell.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for a method for scavenging a fuel cell system.    DESCRIPTION OF DRAWING(S) - The drawing shows a circuit diagram of a fuel cell system.    Fuel cell system (10)    Fuel cell (11)    Hydrogen tank (30)    Temperature sensor (41)    Electronic control unit (45)