To provide an ignition device for a spark ignition engine, capable of preventing generation of misfire when operating at a high load, even if an ignition plug having a large plug gap is used.

A first and a second ignition plugs 10 and 11 for ignition of the air-fuel mixture are inserted into a combustion chamber 11 of a four-cycle engine. A plug gap PG of the second ignition plug 11 is enlarged larger than the plug gap PG of the first ignition plug 10, so that the second ignition plug 11 cannot spark, when operating the four-cycle engine at a high load and that the second ignition plug 11 can spark, when operating the four-cycle engine at low load. When operating the four-cycle engine at a high load, the first ignition plug 10 sparks to secure normal output performance, and the generation of misfire, when operating at a high load can be thereby prevented, independently of the existence of the second plug 11 having the large plug gap PG.