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; and a regeneration treatment unit, which recovers an NOx purification capacity of the NOx reduction type catalyst by lowering an excess-air-ratio of the exhaust gas to a predetermined target excess-air-ratio, wherein the regeneration treatment unit includes: a target setting unit, which sets a target injection amount of at least one of a post injection and an exhaust pipe injection that is required for setting an excess-air-ratio of the exhaust gas to the target excess-air-ratio, based on a suction air amount of the internal combustion engine, the target excess-air-ratio, and a fuel injection amount of the internal combustion engine; and an injection controller, which controls an injection amount of at least one of the post injection and the exhaust pipe injection, based on the target injection amount input from the target setting unit, and the exhaust purification system further comprises: a lambda sensor provided in the exhaust system of the internal combustion engine; and characterized by an injection amount correcting unit, which calculates a learning correction coefficient based on a difference, at a time of a lean operation, between an estimated lambda value estimated from an operating state of the internal combustion engine and an actual lambda value detected by the lambda sensor and corrects the fuel injection amount of the internal combustion engine based on the calculated learning correction coefficient, wherein the target setting unit uses the fuel injection amount corrected by the injection amount correcting unit, as the fuel injection amount of the internal combustion engine. 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; and a regeneration treatment unit, which recovers an NOx purification capacity of the NOx reduction type catalyst by lowering an excess-air-ratio of the exhaust gas to a predetermined target excess-air-ratio, wherein the regeneration treatment unit includes: a target setting unit, which sets a target injection amount of at least one of a post injection and an exhaust pipe injection that is required for setting an excess-air-ratio of the exhaust gas to the target excess-air-ratio, based on a suction air amount of the internal combustion engine, the target excess-air-ratio, and a fuel injection amount of the internal combustion engine; and an injection controller, which controls an injection amount of at least one of the post injection and the exhaust pipe injection, based on the target injection amount input from the target setting unit, and the exhaust purification system further comprises: a lambda sensor provided in the exhaust system of the internal combustion engine; and characterized by an injection amount correcting unit, which calculates a learning correction coefficient based on a difference, at a time of a lean operation, between an estimated lambda value estimated from an operating state of the internal combustion engine and an actual lambda value detected by the lambda sensor and corrects the fuel injection amount of the internal combustion engine based on the calculated learning correction coefficient, wherein the target setting unit uses the fuel injection amount corrected by the injection amount correcting unit, as the fuel injection amount of the internal combustion engine. a target setting unit, which sets a target injection amount of at least one of a post injection and an exhaust pipe injection that is required for setting an excess-air-ratio of the exhaust gas to the target excess-air-ratio, based on a suction air amount of the internal combustion engine, the target excess-air-ratio, and a fuel injection amount of the internal combustion engine; and an injection controller, which controls an injection amount of at least one of the post injection and the exhaust pipe injection, based on the target injection amount input from the target setting unit, and the exhaust purification system further comprises: a lambda sensor provided in the exhaust system of the internal combustion engine; and characterized by an injection amount correcting unit, which calculates a learning correction coefficient based on a difference, at a time of a lean operation, between an estimated lambda value estimated from an operating state of the internal combustion engine and an actual lambda value detected by the lambda sensor and corrects the fuel injection amount of the internal combustion engine based on the calculated learning correction coefficient, wherein the target setting unit uses the fuel injection amount corrected by the injection amount correcting unit, as the fuel injection amount of the internal combustion engine. a lambda sensor provided in the exhaust system of the internal combustion engine; and characterized by an injection amount correcting unit, which calculates a learning correction coefficient based on a difference, at a time of a lean operation, between an estimated lambda value estimated from an operating state of the internal combustion engine and an actual lambda value detected by the lambda sensor and corrects the fuel injection amount of the internal combustion engine based on the calculated learning correction coefficient, wherein the target setting unit uses the fuel injection amount corrected by the injection amount correcting unit, as the fuel injection amount of the internal combustion engine.