In an internal combustion engine, a metal or a metal compound (10) capable of capturing a sulfur component contained in an exhaust gas is provided in a flow path of the exhaust gas. When the amount of the sulfur content captured by the metal or the metal compound (10) is increased as the lapse of time, a physical property of the metal or the metal compound (10) which varies with increase in the amount of the captured sulfur component is measured. Based on the measurement value, the sulfur component in the gas can be detected.