In an ignition coil 2 according to one embodiment, a first outer iron core 360 of a first coil set 10 and a second outer iron core 500 of a second coil set 20 share a common portion 58. The direction of a magnetic flux generated in the common portion 58 upon application of a current flowing through a first primary coil 32 of the first coil set 10 is opposite to the direction of a magnetic flux generated in the common portion 58 upon application of a current flowing through a second primary coil 46 of the second coil set 20. The direction in which an induced current generated in a first secondary coil 34 through an output port 28 is the same as the direction in which an induced current generated in a second secondary coil 48 through the output port 28.