Abstract: An ignition coil for an internal combustion engine includes a core-coil assembly that includes an endless outer ring core, a straight core intersecting the interior of the outer ring core to form a closed magnetic circuit in cooperation with the outer ring core, and a primary coil and a secondary coil concentrically fitted within the outer ring core and supported by the straight core piercing through the primary coil; and an insulation casing that has a bottom at which a high-voltage terminal connected electrically to an ignition plug is retained, supports and accommodates the core-coil assembly therein so that the core-coil assembly is orthogonal to the axis of the plug hole of the engine, and contains a solid layer of insulating resin cast-molded for fixing the core-coil assembly thereto. The secondary coil is ball-shaped and has coil turns that are largest in number at the equator of the ball and gradually decrease toward the opposite poles of the ball.