A vehicle-mounted internal combustion engine controller is provided that can properly stop an internal combustion engine in accordance with an operational state no matter whether a vehicle body is inclined. The vehicle-mounted internal combustion engine controller comprises an inclination sensor for detecting vehicle body inclination; a mechanism for determining the operational state of a combustion engine; and a controller for stopping the operation of the combustion engine in accordance with a vehicle body inclination and an operational state. The cutoff mechanism stops the operation of the vehicle-mounted internal combustion engine when it is judged that a vehicle body inclination angle .alpha. detected by the inclination sensor is greater than a predetermined angle A for a greater or equal period of time as a threshold stop time T1, T2 setting, which varies with the operational state determined by the operational state sensor.