An exhaust purification system comprising: a NOx-occlusion-reduction-type catalyst that is provided in an exhaust passage of an internal combustion engine and occludes NOx in exhaust when the exhaust is in a lean state and reduces and purifies the occluded NOx when the exhaust is in a rich state; a NOx occlusion amount estimation unit that is configured to estimate a NOx occlusion amount in the NOx-occlusion-reduction-type catalyst; first NOx purge control means configured to execute NOx purge of reducing and purifying NOx occluded in the NOx-occlusion-reduction-type catalyst by putting the exhaust into the rich state by repetitively performing, at a predetermined interval, unit fuel injection control comprising injecting a predetermined amount of fuel by at least one of post injection and exhaust pipe injection, in a case where a catalyst temperature of the NOx-occlusion-reduction-type catalyst is equal to or higher than a first catalyst temperature threshold value and a NOx occlusion amount in the NOx-occlusion-reduction-type catalyst is equal to or greater than an occlusion amount threshold value; and second NOx purge control means configured to execute the NOx purge even when the NOx occlusion amount is less than the occlusion amount threshold value, in a case where the catalyst temperature is equal to or higher than a second catalyst temperature threshold value which is greater than the first catalyst temperature threshold value, wherein in the operation of putting the exhaust into the rich state by repetitively performing the unit fuel injection control performed by the first NOx purge control means, a number of fuel injections greater than a number of fuel injections required to reduce and purify an amount of NOx equal to the NOx occlusion amount estimated by the NOx occlusion amount estimation unit is performed, wherein the second NOx purge control means is configured to inject a smaller amount of fuel than an amount of fuel injected in the NOx purge executed by the first NOx purge control means, and wherein the second NOx purge control means is configured to execute fuel injection control of at least one of the post injection and the exhaust pipe injection so as to inject a lowest amount of fuel required to reduce and purify an amount of NOx equal to the NOx occlusion amount estimated by the NOx occlusion amount estimation unit. a NOx-occlusion-reduction-type catalyst that is provided in an exhaust passage of an internal combustion engine and occludes NOx in exhaust when the exhaust is in a lean state and reduces and purifies the occluded NOx when the exhaust is in a rich state; a NOx occlusion amount estimation unit that is configured to estimate a NOx occlusion amount in the NOx-occlusion-reduction-type catalyst; first NOx purge control means configured to execute NOx purge of reducing and purifying NOx occluded in the NOx-occlusion-reduction-type catalyst by putting the exhaust into the rich state by repetitively performing, at a predetermined interval, unit fuel injection control comprising injecting a predetermined amount of fuel by at least one of post injection and exhaust pipe injection, in a case where a catalyst temperature of the NOx-occlusion-reduction-type catalyst is equal to or higher than a first catalyst temperature threshold value and a NOx occlusion amount in the NOx-occlusion-reduction-type catalyst is equal to or greater than an occlusion amount threshold value; and second NOx purge control means configured to execute the NOx purge even when the NOx occlusion amount is less than the occlusion amount threshold value, in a case where the catalyst temperature is equal to or higher than a second catalyst temperature threshold value which is greater than the first catalyst temperature threshold value, wherein in the operation of putting the exhaust into the rich state by repetitively performing the unit fuel injection control performed by the first NOx purge control means, a number of fuel injections greater than a number of fuel injections required to reduce and purify an amount of NOx equal to the NOx occlusion amount estimated by the NOx occlusion amount estimation unit is performed, wherein the second NOx purge control means is configured to inject a smaller amount of fuel than an amount of fuel injected in the NOx purge executed by the first NOx purge control means, and wherein the second NOx purge control means is configured to execute fuel injection control of at least one of the post injection and the exhaust pipe injection so as to inject a lowest amount of fuel required to reduce and purify an amount of NOx equal to the NOx occlusion amount estimated by the NOx occlusion amount estimation unit.