To prevent the overheat of an engine by reducing an NOx emission from the time of the low load operation of the engine through the time of a normal high load operation.

An intake passage 15 supplying air to the cylinder of the engine 12 is connected to the intake port 14 of the engine, and an exhaust passage 17 discharging exhaust gas in the cylinder to the atmosphere is connected to the exhaust port 16 of the cylinder. An external EGR system 21 has an EGR passage 21a with one end connected to the exhaust passage and the other end connected to the intake passage, and an EGR valve 21b capable of opening/closing the EGR passage. An internal EGR system is formed to introduce exhaust gas from the exhaust passage to the cylinder by opening an exhaust valve opening/closing the exhaust port at the time of intake stroke of the cylinder. An EGR cooler 21c cooling exhaust gas by cooling water for the engine is provided in the EGR passage, and a controller controls the external EGR system based on output detected by a temperature sensor 45.