An exhaust purification system comprising: an NOx reduction type catalyst, which is provided in an exhaust system of an internal combustion engine and reduces and purifies NOx in an exhaust gas; a temperature acquisition unit, which acquires an estimated catalyst temperature of the NOx reduction type catalyst; and a regeneration treatment unit, which executes a catalyst regeneration to recover an NOx purification capacity of the NOx reduction type catalyst, wherein the regeneration treatment unit alternately executes a rich control, in which an exhaust air fuel ratio is set to a rich state to raise a temperature of the NOx reduction type catalyst to a predetermined target temperature, and a lean control, in which the exhaust air fuel ratio is set to a lean state to lower the temperature of the NOx reduction type catalyst, wherein the regeneration treatment unit sets an execution period of the lean control by a PID control, based on a deviation between the catalyst temperature acquired by the temperature acquisition unit at a timing at which the previous rich control is switched from an on state to an off state, and the target temperature, characterized in that: the regeneration treatment unit executes the rich control by using a post injection or an exhaust pipe injection, and sets a post injection amount or an exhaust pipe injection amount based on an intake air amount of the internal combustion engine, a predetermined target excess-air-ratio, and a fuel injection amount of the internal combustion engine; and the regeneration treatment unit sets a value, which is obtained by subtracting the fuel injection amount of the internal combustion engine from a value obtained by dividing the intake air amount of the internal combustion engine by the target excess-air-ratio, a fuel specific gravity, and a theoretical air-fuel ratio, as the post injection amount or the exhaust pipe injection amount. an NOx reduction type catalyst, which is provided in an exhaust system of an internal combustion engine and reduces and purifies NOx in an exhaust gas; a temperature acquisition unit, which acquires an estimated catalyst temperature of the NOx reduction type catalyst; and a regeneration treatment unit, which executes a catalyst regeneration to recover an NOx purification capacity of the NOx reduction type catalyst, wherein the regeneration treatment unit alternately executes a rich control, in which an exhaust air fuel ratio is set to a rich state to raise a temperature of the NOx reduction type catalyst to a predetermined target temperature, and a lean control, in which the exhaust air fuel ratio is set to a lean state to lower the temperature of the NOx reduction type catalyst, wherein the regeneration treatment unit sets an execution period of the lean control by a PID control, based on a deviation between the catalyst temperature acquired by the temperature acquisition unit at a timing at which the previous rich control is switched from an on state to an off state, and the target temperature, characterized in that: the regeneration treatment unit executes the rich control by using a post injection or an exhaust pipe injection, and sets a post injection amount or an exhaust pipe injection amount based on an intake air amount of the internal combustion engine, a predetermined target excess-air-ratio, and a fuel injection amount of the internal combustion engine; and the regeneration treatment unit sets a value, which is obtained by subtracting the fuel injection amount of the internal combustion engine from a value obtained by dividing the intake air amount of the internal combustion engine by the target excess-air-ratio, a fuel specific gravity, and a theoretical air-fuel ratio, as the post injection amount or the exhaust pipe injection amount. the regeneration treatment unit executes the rich control by using a post injection or an exhaust pipe injection, and sets a post injection amount or an exhaust pipe injection amount based on an intake air amount of the internal combustion engine, a predetermined target excess-air-ratio, and a fuel injection amount of the internal combustion engine; and the regeneration treatment unit sets a value, which is obtained by subtracting the fuel injection amount of the internal combustion engine from a value obtained by dividing the intake air amount of the internal combustion engine by the target excess-air-ratio, a fuel specific gravity, and a theoretical air-fuel ratio, as the post injection amount or the exhaust pipe injection amount.