In an apparatus for controlling the energization time of an ignition coil of an internal combustion engine, a desired ignition timing is computed in accordance with a load and rotation speed of the engine and an energization starting time of the ignition coil is computed in accordance with the ignition timing. The energization starting time is retarded in accordance with the primary current through the ignition coil and the energization time of the ignition coil is reduced. The primary current flow through the ignition coil is interrupted at the ignition timing.