To provide a combustion improving method to improve combustion efficiency by simply modifying an existing diesel engine, a gasoline engine, a jet engine, and a boiler, remarkably improve a horse power and fuel consumption, and reduce an exhaust amount of a toxic component, such as HC and CO2, in exhaust gas.

A combustion improving method of a diesel engine, a gasoline engine, a jet engine, and a boiler, involves such a structure that fuel is vaporized by the heat of exhaust gas, the gas is mixed with air, the mixture is fed to the engine through an air inlet and mixed with liquid fuel for combustion. This constitution remarkably improve a horse power since complete combustion is executed by mixing together gas fuel, vaporized by an exhaust gas heat, and liquid fuel, and eminently reduces an exhaust amount of a toxic component, such as HC and CO2, in exhaust gas.