IGNITION SYSTEM

An ignition system includes a dividing wall (34) which divides a combustion chamber (30) of an engine (90) into a main chamber (31) and a pre-chamber (38) and has formed therein at least one spray hole (35) which communicates between the main chamber and the pre-chamber, and a spark plug (40) in which voltage is applied across a spark gap (45) between a first electrode (44) and a second electrode (46) to create an electrical spark (f) to ignite fuel. The pre-chamber has the first electrode. The dividing wall or a member which electrically conducts with the dividing wall has the second electrode. The ignition system executes an after-top-dead-center ignition control mode to ignite fuel after a compression stroke top dead center (Td). In the after-top-dead-center ignition control mode, an ignition source which is in the form of a self-growable flame kernel is provided in a spray hole-nearby region (R), the spray hole, or the main chamber within a crank angle of 20° after an ignition timing (Ts) at which the voltage starts to be applied across the spark gap. The spray hole-nearby region is a region which is located 3mm or less away from a spray hole center in the pre-chamber.