An exhaust gas purification device for an internal combustion engine is equipped with a first NOx selective reduction catalyst, which is provided inside the engine exhaust path and selectively reduces NOx by supplying a reducing agent, a second NOx selective reduction catalyst, which is provided in the engine exhaust path on the downstream side of the first NOx selective reduction catalyst and selectively reduces NOx by supplying a reducing agent, and a reducing agent supply device that supplies a reducing agent to the first NOx selective catalyst. The amount of reducing agent adsorbed onto the second NOx selective reducing catalyst is estimated, and the amount of reducing agent supplied from the reducing agent supply device is adjusted so that the estimated amount of adsorbed reducing agent does not exceed an allowed value.