IGNITION DEVICE AND IGNITION METHOD FOR INTERNAL COMBUSTION ENGINE

An ignition unit (4) of an internal combustion engine (1) is equipped with an ignition coil (21) including a primary coil (21a) and a secondary coil (21b), an igniter (22), and a secondary current detection resistor (23). By means of the secondary current detection resistor (23), an engine controller (10) detects a current value (Idis) of the secondary current immediately after completion of capacitive discharge. The current value (Idis) is correlated with a gas pressure between electrodes at ignition timing, and thus an in-cylinder pressure (Pign) can be estimated from the current value (Idis). An amount of time-dependent change (µ) in compression ratio, caused by accumulation of deposits, is calculated based on the in-cylinder pressure (Pign) at the ignition timing.