An ignition coil for an internal combustion engine comprises a primary coil, a secondary coil, a center core, an outer peripheral core, a coil case, seal rubber, a pole joint, and a plug cap. The coil case has: a receiving section for receiving the primary coil, the secondary coil, the center core, and the outer peripheral core and disposed outside a plug hole in a cylinder of an internal combustion engine, the plug hole having an ignition plug received therein; and a high-voltage tower section protruding from the receiving section and disposed within the plug hole. The pole joint is disposed within the plug hole and mounted to the high-voltage tower section through the seal rubber. The pole joint is provided with a rib protruding to the outer periphery and facing the inner peripheral surface of the plug hole. The inner peripheral side of the rib faces the high-voltage tower section with the seal rubber therebetween.