PURPOSE: To prevent sintering due to heat and prolong the life of a combustion catalyst having a honeycomb structure by constituting passages for fluid of the catalyst in such a manner that walls of passages consist of walls having an active material to cause the catalytic reaction and walls having no active material and that the area of walls having the active material is ≤1/2 of the whole walls.

CONSTITUTION: The combustion catalyst having a honeycomb structure is formed in such a manner that walls of passages for fluid consist of walls having an active material which causes the catalytic reaction and walls having no active material and that the area of walls having the active material is ≤1/2 of the whole walls. On the wall 4 having the active material, the combustion reaction is promoted by the active material and thereby, the wall 4 is heated. On the other hand, on the wall 5 having no active material, the combustion reaction does not proceed so that the wall 5 gives an effect to remove the combustion heat generating on the wall 4 having the active material which is on the back of the wall 5. Thereby, the wall 4 having the active material is cooled on the back, which prevents local temp. increase.