There is provided an ignition or plasma generation apparatus that eliminates the need for resonance means in a combustion chamber and simplifies the electrode structure within the combustion chamber in an instance where energy from each of a spark discharge and microwaves is used to ignite an air-fuel mixture gas in an internal combustion engine. The ignition or plasma generation apparatus includes a mixing circuit for mixing a high-voltage pulse from a high-voltage pulse generator and microwave energy from a microwave generator; and an ignition plug into which an output from the mixing circuit is supplied, the plug used for introducing the output into a combustion chamber of an internal combustion engine. The output supplied from the mixing circuit to the ignition plug is supplied in a manner in which the microwave energy and the high-voltage pulse are superimposed on each other on a same transmission line.