An air supply device for a fuel cell is disclosed which is provided with a displacement compressor (10) for supplying pressurized air as an air source to a cathode through an air supply line connected to the cathode inlet side of the fuel cell (I) so that a burned gas obtained by burning an anode exhaust gas (AG) discharged from an anode of the fuel cell may be conducted to the intake side of an exhaust gas turbine (8) for driving the displacement compressor, and so that air may be supplied to the cathode (2) by driving the displacement compressor (10) with the exhaust gas turbine that operates with the burned gas of the anode exhaust gas. A heat exchanger (22) vaporizes fuel fed to the anode of the fuel cell. The heat exchanger takes in exhaust gas from the turbine and outputs a high temperature exhaust gas, which is conducted to the intake of the turbine.