An exhaust purification system can prevent a NH3 slip caused by an excessive injection of urea water, and includes: an SCR that purifies NOx contained in an exhaust gas using ammonia, as a reducing agent, produced from urea water; a urea water injection device that injects the urea water into an exhaust passage upstream from the SCR; an estimated-adsorption-amount calculation unit that calculates an estimated adsorption amount of the ammonia adsorbed in the SCR; an injection control unit that executes an injection control of the urea water injection device based on the estimated adsorption amount; and an estimated-adsorption-amount change unit that changes the estimated adsorption amount used for the injection control into a value increased or decreased by a predetermined amount when a predetermined condition is established that can cause a difference between an actual adsorption amount of the ammonia adsorbed in the SCR and the estimated adsorption amount.