An ignition coil includes primary and secondary coils, a center core inserted into a center hole of the primary coil and a center hole of the secondary coil, an annular side core that forms a magnetic circuit through which a first magnetic flux A generated by the primary coil by being joined to the center core permeates, and a permanent magnet that is disposed between the center core and the side core and that emits a second magnetic flux B directed opposite to the first magnetic flux A to apply a magnetic bias. The side core includes protruded portions that protrude towards lateral sides of a T-shaped horizontal portion of the center core, and gaps are provided between the lateral sides of the T-shaped horizontal portion of the center core and the protruded portions of the side core.