PURPOSE: To improve combustion efficiency by supplying a cylinder with ozone produced by an ozone generator.

CONSTITUTION: An ozone generator consists of a main body part 1 and an electric control part 2, and an opening 3' of the main body part 1 is connected to the atmosphere through a filter 4. A fan 5 and a fan motor 6 are accommodated in the rear part of a casing 3, and at the same time an ozone generating electrode consisting of a plurality of thin plate cores 7 and a cylindrical core 8 is accommodated in the fore part of the casing 3. The tip of the casing 3 is connected with an air cleaner A via a conduit 14. Generated ozone is sent forcibly by the fan 5 into the air cleaner A in order to improve combustion efficiency.