Lean fuel sucking gas turbine system

Provided is a lean fuel sucking gas turbine system comprising a compressor (1) for compressing a mixed gas (G1) having a fuel and air mixed to a concentration of an inflammable limit or lower, thereby producing a compressed gas (G2), a first catalyst combustor (2) for burning the compressed gas (G2) by a catalyst reaction, a turbine (3) adapted to be driven by a combustion gas (G3) from a second catalyst combustor (9), and a reproducer (6) for heating the compressed gas (G2) to be introduced into the first catalyst combustor (2) with an exhaust gas (G4) from the turbine (3). Between the turbine (3) and the reproducer (6), there is arranged a duct burner (7) for flame-burning a first auxiliary fuel (F1) in the exhaust gas (G4). Thus, it is possible to attain efficient operation of the system while simplifying the entire constitution and to prevent the blow-by of the mixed gas.