Abstract: The present invention relates to a fixing structure of an exhaust gas after-treatment device in an agricultural working vehicle, which makes it easy to attach or detach the exhaust gas after-treatment device to or from an engine according to requirements, and can improve the usability in the internal space of the engine room. To this end, the present invention provides a structure for fixing an exhaust gas after-treatment device purifying the exhaust gas of an engine to the engine in an agricultural working vehicle, characterized in that the exhaust gas after-treatment device is arranged on the top of the flywheel housing of the engine in the direction perpendicular to the longitudinal direction of the engine, and is fixed simultaneously to both the cylinder block of the engine and the flywheel housing by means of a fixing member.