To prevent from incorrectly diagnosing abnormality/normality of a cooling system by difference in behavior of cooling water temperature dependent on execution of energization to a block heater during engine stopping.

When operation of the engine 11 is stopped, the cooling water temperature detected by a cooling water temperature sensor 32 is stored in a backup RAM 45 as the cooling water temperature in engine stopping. At a time point when a predetermined time elapsed from the time of engine stopping, an ECU 41 is power on and is self-started to perform leak diagnosis of an evaporation-purge system and the cooling water temperature detected in the self-starting is stored as the cooling water temperature in self-starting in the backup RAM 45. Then, execution of energization to the block heater 34 is determined in engine starting by reading in a temperature difference between the cooling water temperature in engine stopping and the cooling water temperature in self-starting or the like from the backup RAM 45 and comparing it with a determination value and if energization to the block heater 34 is found to have been executed, abnormality diagnosis of the cooling system is prohibited.