An exhaust gas control apparatus for an internal combustion engine is provided with an exhaust catalyst disposed in an exhaust passage (4) of the internal combustion engine, a concentration detection unit (10) that is capable of detecting a total concentration of a sulfur oxide and a hydrogen sulfide contained in an exhaust gas that passes through the exhaust catalyst, and detecting a concentration of the sulfur oxide, and a sulfur concentration estimation unit (15) that estimates a concentration of sulfur contained in a fuel based on a detection value of the concentration detection unit (10) when it is determined that the exhaust gas is at one of a stoichiometric and rich air/fuel ratio.