It is an object of the present invention to provide an exhaust gas treatment device of an engine capable of preventing matching surfaces of catalyst portions configuring a combustible gas catalyst from being thermally damaged. In the exhaust gas treatment device, combustible gas is produced by combustible gas generating catalyst, exhaust gas heated by combustion of combustible gas is supplied to an exhaust gas treatment portion, the combustible gas generating catalyst comprises an aggregate of a plurality of catalyst portions, each of the catalyst portions includes a matching surface with respect to adjacent one of the catalyst portions, a fastening ring is fitted over the combustible gas generating catalyst in which the matching surfaces of the adjacent catalyst portions are abutted against each other, and the matching surfaces of the adjacent catalyst portions are brought into tight contact with each other by a fastening force of the fastening ring.