An ignition apparatus is received in a plug hole (43a) which is formed by a cylinder head (41a) and a cylinder head cover (42a) of an internal combustion engine. A side core (18) has a slit between two horizontally extending side wall ends. The side core (18) comprises one selected from a laminated sheet structure comprised of two grain oriented silicon steel sheets, each having a slit between two horizontally extending side wall ends, and the plural slits align at a substantially same position. The slit prevents an one-turn short of a magnetic flux of the side core (18), thereby a predetermined secondary voltage more than an engine requirement secondary voltage is obtained. An ignitor reception portion comprises an independent and individual ignitor reception portion and an independent and individual coil reception portion, and the ignitor reception portion and the coil reception portion are combined.