a case cylinder connected to a diesel engine via an exhaust pipe having an exhaust stream enhance part and an exhaust stream exit part;

a filter arranged inside said case cylinder for circulating discharged exhaust from said diesel engine and trapping particular matter in said exhaust;

an exothermic catalyst having a low temperature exothermic catalyst of precious metal and a medium temperature exothermic catalyst of a base metal in a state of mixed dispersion thereof on said filter; and

a retention structure for retaining said exothermic catalyst and said filter in said case cylinder,

wherein said retention structure includes:

an inner retention cylinder which extends along an axis direction of said case cylinder and forms at last one communicative connection passageway enabling outflow of exhaust radially outward; and

a star-shaped outer retention cylinder which has alternately a plurality of mountain-shaped parts and a plurality of valley-shaped parts, said star-shaped outer retention cylinder being arranged radially outward of said inner retention cylinder and being formed with micro-spaces to flow the exhaust from an inside thereof to an outside thereof, an inner side and an outer side of said star-shaped outer retention cylinder being shaped like a star and sandwiching a fiber for further trapping residual particulate matter passing through said filter;

wherein the filter with the exothermic catalyst is arranged between said inner retention cylinder and said star-shaped outer retention cylinder, and

wherein said low and medium temperature exothermic catalyst coexists on said filter shaped like a star corresponding to said star-shaped outer retention cylinder, being urged toward said inner retention cylinder by elastic force of said fiber of said outer retention cylinder.