A variable-nozzle type turbo charger capable of temporarily decreasing the back pressure of the engine at the start of the engine. The turbo charger is equipped with a plurality of nozzle vanes of which the opening degree can be changed and are capable of changing the areas of turbine nozzles at the time when exhaust gases of an engine are guided from said turbine nozzles formed among said nozzle vanes to a turbine rotor, wherein an actuator that adjusts the opening degree of the nozzle vanes is so controlled that the areas of the turbine nozzles are larger than a minimum area for a predetermined period of time from the start of the engine, and, after the passage of said predetermined period of time, said actuator is so controlled that the areas of said turbine nozzles become the minimum area to promote the warming-up of the engine when the water temperature of the engine or the engine load is smaller than a predetermined value.