A metal or metal compound (10) able to trap a sulfur component in exhaust gas is arranged in a flow passage of exhaust gas in an internal combustion engine. When the amount of sulfur component trapped in the metal or metal compound (10) increases over the passage of time, a property of the metal or metal compound (10) which changes along with the increase in the amount of trapped sulfur component is measured and the sulfur component in the gas is detected from the measured property.
