The present invention aims at providing a technology capable of increasing a heat quantity of a combustion gas discharged from a combustion heater in an internal combustion engine having the combustion heater. To accomplish this object, the internal combustion engine having the combustion heater comprises a combustion chamber (17d) for combusting a fuel, an engine cooling water circulating between the combustion chamber (17d) and an engine-related element, a heat exchange unit (17a, 17c, 150) for performing a heat exchange between the engine cooling water and a combustion gas produced in the combustion chamber (17d), and heat exchange rate decreasing means (149, 205) for decreasing a heat exchange rate in said heat exchange unit (17a, 17c, 150).