Abstract: There is disclosed an ignition system for an internal combustion engine wherein insertion of a terminal (41) into a sleeve (55) from above a cap (51), with an upper portion of the sleeve (55) fitted in a sleeve receiving portion (51b) of the cap (51), causes a ledge (42) on an upper portion of the terminal (41) to advance beyond a ledge (53) of the cap (51) made of rubber into a position lower than the ledge (53), whereby an upper side of the ledge (42) engages the ledge (53) to prevent the upward movement of the terminal (41) and a lower side of the ledge (42) is locked to an upper end surface of the sleeve (55) to prevent the terminal (41) from slipping off downwardly, thereby completely positioning the terminal (41).