Provided is an exhaust gas purification system for a construction machine that can prevent deterioration of an aqueous urea solution remaining in a conduit of an aqueous urea solution replenishing circuit after replenishing an aqueous urea solution tank with the aqueous urea solution due to an influence of heat generated in an engine, a hydraulic fluid tank, and the like. An aqueous urea solution return circuit 202 that returns, to an aqueous urea solution tank 6, an excessive aqueous urea solution that has not been injected from an aqueous urea solution injection device 4 into exhaust gas is provided with a first return conduit 9 that connects the aqueous urea solution injection device 4 to the aqueous urea solution tank 6 and a second return conduit 10 that connects the aqueous urea solution injection device 4 to a conduit 11 of an aqueous urea solution replenishing circuit 201, and an injection valve opening pressure of a first check valve 15 provided in the first return conduit 9 is set higher than an inj
