A detection device for an internal combustion engine is preferably applied to the internal combustion engine which includes a temperature varying member, which is provided in an exhaust system, and whose temperature varies due to gas flow in the exhaust system. A temperature correlation value detection unit detects a correlation value which correlates with the temperature of the temperature varying member. The term correlation value herein includes impedance of the temperature varying member, a signal output value such as current and voltage output sent from the temperature varying member, and/or the temperature varying member's own temperature. A variation calculating unit calculates a variation of the correlation value, in a time period when the gas flow arises, detected by the temperature correlation value detection unit.