EXHAUST PURIFICATION SYSTEM

It effectively suppresses an unstable combustion of an engine at a time of start or end of catalyst regeneration. The exhaust purification system includes: an NOx reduction type catalyst (32) which is provided in an exhaust passage of an internal combustion engine; a intake air amount sensor (40) which detects a intake air amount of the internal combustion engine; and a controller (50) which executes a regeneration treatment that switches an exhaust air fuel ratio from a lean state to a rich state by using an air-system control to reduce the intake air amount and an injection-system control to increase a fuel injection amount, which are used in combination. The controller (50) changes at least one of a fuel injection timing and the fuel injection amount in the internal combustion engine (10) in response to a detection value of the intake air amount sensor (40) in at least one period of switching of: a period of switching the lean state where the regeneration treatment is started to the rich state and a period of switching the rich state where the regeneration treatment is ended to the lean state.