An exhaust purification system that includes a selective catalytic reduction to purify NOx contained in an exhaust gas by using ammonia produced from urea water and an NOx sensor to acquire a value of the NOx contained in the exhaust gas, and the exhaust purification system includes: a reach time measurement unit that measures a reach time of the NOx value acquired by the NOx sensor, the reach time being a required time for the NOx value to reach, from a first predetermined determinative NOx value, a second predetermined determinative NOx value, which is higher than the first determinative NOx value; and a determination unit that determines that malfunction occurs in the NOx sensor when the reach time measured by the reach time measurement unit is equal to or shorter than a first predetermined determinative time.
