A control method of an internal combustion engine, comprising: a step of computing a temperature of an exhaust gas (Tex) on the basis of a rotating speed, a charging efficiency, an ignition timing, an equivalent ratio, an external EGR rate, an exhaust valve opening timing, and a supercharging pressure; a step of computing an estimation value of a temperature (Tw) of an exhaust heat exchanger on the basis of the exhaust gas temperature (Tex), an amount of an intake air, a temperature of a cooling medium or a heat medium of said exhaust heat exchanger, a flow rate of the cooling medium or the heat medium of said exhaust heat exchanger; a step of setting a target value of said exhaust heat exchanger temperature (Tw); and a step of transiently correcting at least one of the ignition timing, the equivalent ratio, the external EGR rate, and the exhaust valve opening timing, on the basis of the estimation value and said target value, wherein an intake valve and an exhaust valve have a variable valve mechanism (11, 12) varying a phase, a lift and an operating angle, and a power generator connected to a crank shaft of said internal combustion engine is provided, and the method computes a total of a heat supply amount and an electric power supply amount and a thermoelectric ratio corresponding to a ratio between the heat supply amount and the electric power supply amount obtained from said power generator, and an amount of heat obtained via said exhaust heat exchanger, and wherein an intake valve closing timing is changed from a bottom dead center while fixing an intake valve opening timing to the vicinity of a top dead center by the variable valve mechanism of said intake value on the basis of said total of the heat supply amount and the electric power supply amount, and an exhaust valve opening timing is changed from a bottom dead center while fixing an exhaust valve closing timing to the vicinity of a top dead center by the variable valve mechanism of said exhaust valve on the basis of said thermoelectric ratio. a step of computing a temperature of an exhaust gas (Tex) on the basis of a rotating speed, a charging efficiency, an ignition timing, an equivalent ratio, an external EGR rate, an exhaust valve opening timing, and a supercharging pressure; a step of computing an estimation value of a temperature (Tw) of an exhaust heat exchanger on the basis of the exhaust gas temperature (Tex), an amount of an intake air, a temperature of a cooling medium or a heat medium of said exhaust heat exchanger, a flow rate of the cooling medium or the heat medium of said exhaust heat exchanger; a step of setting a target value of said exhaust heat exchanger temperature (Tw); and a step of transiently correcting at least one of the ignition timing, the equivalent ratio, the external EGR rate, and the exhaust valve opening timing, on the basis of the estimation value and said target value, wherein an intake valve and an exhaust valve have a variable valve mechanism (11, 12) varying a phase, a lift and an operating angle, and a power generator connected to a crank shaft of said internal combustion engine is provided, and the method computes a total of a heat supply amount and an electric power supply amount and a thermoelectric ratio corresponding to a ratio between the heat supply amount and the electric power supply amount obtained from said power generator, and an amount of heat obtained via said exhaust heat exchanger, and wherein an intake valve closing timing is changed from a bottom dead center while fixing an intake valve opening timing to the vicinity of a top dead center by the variable valve mechanism of said intake value on the basis of said total of the heat supply amount and the electric power supply amount, and an exhaust valve opening timing is changed from a bottom dead center while fixing an exhaust valve closing timing to the vicinity of a top dead center by the variable valve mechanism of said exhaust valve on the basis of said thermoelectric ratio. an intake valve and an exhaust valve have a variable valve mechanism (11, 12) varying a phase, a lift and an operating angle, and a power generator connected to a crank shaft of said internal combustion engine is provided, and the method computes a total of a heat supply amount and an electric power supply amount and a thermoelectric ratio corresponding to a ratio between the heat supply amount and the electric power supply amount obtained from said power generator, and an amount of heat obtained via said exhaust heat exchanger, and wherein an intake valve closing timing is changed from a bottom dead center while fixing an intake valve opening timing to the vicinity of a top dead center by the variable valve mechanism of said intake value on the basis of said total of the heat supply amount and the electric power supply amount, and an exhaust valve opening timing is changed from a bottom dead center while fixing an exhaust valve closing timing to the vicinity of a top dead center by the variable valve mechanism of said exhaust valve on the basis of said thermoelectric ratio.