PURPOSE: To increase combustion efficiency of light or heavy oil by using magnetic force.

CONSTITUTION: Two pieces of anisotropic permanent magnet 3 in the shape of semi-circle or a horseshoe, having magnetic flux above 500 gausses and below 3,000 gausses are straddled across the same side of a pipe, of which external diameter is 6W90mm and its length is 100W1,000mm. The magnets are fixed to the pipe in the manner that the distance between both magnet is 30W500mm, and the axis of a pipe 1 comes to the level of surfaces which constitutes the faces of polar ends of both magnets. With such a structure, consumption of fuel is saved, the life of an engine is elongated, while reducing the deterioration of an engine oil. In addition, nitrogen oxide, sulfur oxide and the like are prevented from being produced in the exhaust gas.