EXHAUST SYSTEM STATE DETECTION DEVICE

The invention relates to an exhaust system state detection device that has a simple configuration and can effectively detect an exhaust gas temperature. The exhaust system state detection device includes an intake air oxygen concentration sensor (32) that detects an oxygen concentration of an intake air of an engine (10), an engine revolution sensor (30) and an accelerator position sensor (31) that in combination detect a running condition, an indicated thermal efficiency calculation unit (42) that calculates an amount of change in the indicated thermal efficiency of the engine (10) based on the intake air oxygen concentration, the fuel injection start timing, and a pre-stored first model formula defining the relation among the intake air oxygen concentration, the injection start timing, and the amount of change in the indicated thermal efficiency, and an exhaust gas temperature calculating unit (43) that calculates an exhaust gas temperature of the engine (10) based on the amount of change in the indicated thermal efficiency and a pre-stored second model formula defining the relation between the exhaust gas temperature and the amount of change in the indicated thermal efficiency.