In order to facilitate the execution of delicate work to be executed with the help of engine sound, disclosed is an exhaust gas purification system for a working machine, said exhaust gas purification system being provided with an engine (70) mounted in the working machine (140), an exhaust gas purification device (50) disposed in an exhaust system (77) of the engine (70), and a regeneration device (70, 81, 82, 117) for removing particulate matter in the exhaust gas purification device (50) by combustion. When the clogging state of the exhaust gas purification device (50) reaches a prescribed level or higher, the regeneration device (70, 81, 82, 117) is made operable. The exhaust gas purification system is further provided with a regeneration permission input means (21) for permitting the operation of the regeneration device (70, 81, 82, 117), and a rotation speed maintenance input means (27) for maintaining the rotation speed (N) of the engine (70) at a predetermined rotation speed (Nm). When the rotation speed maintenance input means (27) is turned on while the permission operation of the regeneration permission input means (21) is being performed, the rotation speed maintenance operation of the engine (70) is executed prior to the operation of the regeneration device (70, 81, 82, 117).