A plasma generating device for an internal combustion engine sets the generating-atmosphere pressure for generating plasma to the intake pressure, thereby achieving a reduction in the size, weight, and energy consumption of the plasma generating device and an improvement in combustibility. An internal combustion engine includes a throttle valve arranged in an intake passage having an intake opening that opens to a combustion chamber. An intake valve opens and closes the intake opening. A plasma generating device includes a plasma generator having a generating chamber for converting intake air into a plasma state to generate plasma. The plasma generating device supplies plasma to a downstream passage of the intake passage between the throttle valve and the intake valve. A gas control valve operates in conjunction with the throttle valve, and is arranged in an introduction passage between a clean chamber of the air cleaner chamber and a generating chamber.