A lean fuel sucking gas turbine is provided with: a compressor (1) which compresses working gas (G1) with varying fuel concentration at a combustible concentration limit or lower to generate compressed gas (G2); a catalytic combustor (2) which burns the compressed gas (G2) by a catalytic reaction; a turbine (3) which is driven by combustion gas (G3) from the catalytic combustor (2); a heat exchanger (6) which heats the compressed gas (G2) introduced from the compressor (1) to the catalytic combustor (2) by exhaust gas (G4) from the turbine (3); a heat exchange bypass valve (40) which causes the inlet side and the outlet side of the compressed gas (G2) of the heat exchanger (6) to communicate with each other; and a first catalyst outlet temperature control unit (47) which opens the heat exchange bypass valve (40) when the outlet temperature of the catalytic combustor (2) reaches an outlet prescribed value or more.
