An internal combustion engine controller, comprising: a voltage boost circuit for supplying a switching current from a battery power supply (1, 210) to a voltage boost coil and storing, into a voltage boost capacitor through a charging diode, a high voltage generated in the boost coil when a level of the switching current is reduced and during a voltage boost switching operation the energy stored in the voltage boost coil is moved to the voltage boost capacitor, an overboost-compensating controller for changing the level of an overboost-compensating signal; a driving circuit for driving an injector current using the high voltage stored within the boost capacitor and regenerating electrical energy of an injector to said voltage boost circuit when a level of the injector current is reduced; and a discharge switching element for being provided in parallel to the charging diode; wherein, if the high voltage stored within said voltage boost circuit exceeds a required overboost compensation starting voltage, said overboost-compensating controller controls that said discharge switching element is electrically energized to discharge the high voltage into the battery power supply (1, 210) through the boost coil, characterised in that, if the high voltage stored within said voltage boost circuit exceeds a required overboost compensation starting voltage, when voltage boost switching operation is in progress, said overboost-compensating controller controls that electrical energizing of said discharge switching element is suppressed, and after the voltage boost switching operation, said overboost-compensating controller controls that said discharge switching element is energized to discharge the high voltage into the battery power supply (1, 210) through the boost coil. a voltage boost circuit for supplying a switching current from a battery power supply (1, 210) to a voltage boost coil and storing, into a voltage boost capacitor through a charging diode, a high voltage generated in the boost coil when a level of the switching current is reduced and during a voltage boost switching operation the energy stored in the voltage boost coil is moved to the voltage boost capacitor, an overboost-compensating controller for changing the level of an overboost-compensating signal; a driving circuit for driving an injector current using the high voltage stored within the boost capacitor and regenerating electrical energy of an injector to said voltage boost circuit when a level of the injector current is reduced; and a discharge switching element for being provided in parallel to the charging diode; wherein, if the high voltage stored within said voltage boost circuit exceeds a required overboost compensation starting voltage, said overboost-compensating controller controls that said discharge switching element is electrically energized to discharge the high voltage into the battery power supply (1, 210) through the boost coil, characterised in that, if the high voltage stored within said voltage boost circuit exceeds a required overboost compensation starting voltage, when voltage boost switching operation is in progress, said overboost-compensating controller controls that electrical energizing of said discharge switching element is suppressed, and after the voltage boost switching operation, said overboost-compensating controller controls that said discharge switching element is energized to discharge the high voltage into the battery power supply (1, 210) through the boost coil.