PURPOSE: To prevent an abnormal rise of pressure within a cylinder of an internal-combustion engine by providing a controller for feeding an energizing signal to an intake air heater when the value of a temperature detector is below a given level and the outputs of an engine speed detector and a load detector and above given values.

CONSTITUTION: The governor of a fuel injection pump 8, the speed change gear of an engine 10, and an intake air passage 9 are provided with an engine load detector 2, a revolution detector 3, and an intake air temperature detector 4, respectively. The values detected by these detectors 2W4 are input to a controller 5. This feeds an energizing signal to an intake air heater 7 when the value of the intake air temperature detector 4 is below a given level and the output values of the revolution detector 3 and the engine load detector 2 are above given levels. Thus, an abnormal rise of the pressure within a cylinder is prevented when an intake air temperature is decreased.