A method of activating a catalyst for a fuel cell in order to perform catalyst activation in a cathode electrode of the fuel cell includes a first process in which hydrogen is supplied into an anode electrode, the side of an air supply line of the cathode electrode is sealed, and the side of an air exhaust line of the cathode electrode is opened to an atmosphere, a second process in which the side of the air exhaust line of the cathode electrode is sealed after the first process, and a third process in which catalyst activation is performed in the cathode electrode after the second process.