A fuel injection device for a combustor of a gas turbine, the fuel injection device comprising: a pilot fuel injector disposed on an axis of the fuel injection device; a main fuel injector having an annular shape and disposed so as to be concentric with the pilot fuel injector and encircle an outer periphery of the pilot fuel injector; a passage wall that forms a main air passage configured to introduce an air to be mixed with a fuel injected from the main fuel injector in a radial direction, the passage wall having an opening configured to introduce the fuel from the main fuel injector into the main air passage; a plurality of main fuel injection holes that are formed in the main fuel injector so as to be spaced circumferentially from each other and are configured to inject the fuel axially rearward; a main fuel injection nozzle protruding axially rearward from a circumference of the main fuel injection hole so as to face the opening of the passage wall, and configured to guide the fuel to the main air passage; a heat-shielding casing covering the main fuel injector and having a through-hole that allows the main fuel injection nozzle to penetrate therethrough, at least a portion of the heat-shielding casing being spaced axially from the passage wall; characterized by a ring member interposed in an axial gap defined between the passage wall and the heat-shielding casing, the ring member covering a through-hole gap defined between the main fuel injection nozzle and an inner peripheral surface of the through-hole, and having a purge passage communicated with the opening of the passage wall and configured to introduce an air within the axial gap as an air for fuel purge into the main air passage. a pilot fuel injector disposed on an axis of the fuel injection device; a main fuel injector having an annular shape and disposed so as to be concentric with the pilot fuel injector and encircle an outer periphery of the pilot fuel injector; a passage wall that forms a main air passage configured to introduce an air to be mixed with a fuel injected from the main fuel injector in a radial direction, the passage wall having an opening configured to introduce the fuel from the main fuel injector into the main air passage; a plurality of main fuel injection holes that are formed in the main fuel injector so as to be spaced circumferentially from each other and are configured to inject the fuel axially rearward; a main fuel injection nozzle protruding axially rearward from a circumference of the main fuel injection hole so as to face the opening of the passage wall, and configured to guide the fuel to the main air passage; a heat-shielding casing covering the main fuel injector and having a through-hole that allows the main fuel injection nozzle to penetrate therethrough, at least a portion of the heat-shielding casing being spaced axially from the passage wall; characterized by a ring member interposed in an axial gap defined between the passage wall and the heat-shielding casing, the ring member covering a through-hole gap defined between the main fuel injection nozzle and an inner peripheral surface of the through-hole, and having a purge passage communicated with the opening of the passage wall and configured to introduce an air within the axial gap as an air for fuel purge into the main air passage.