PURPOSE: To reduce a nitrogen oxide quantity in an internal combustion engine such as a diesel engine, a gasoline engine, etc.

CONSTITUTION: The base part of a liquid flow tube 2 to which first and second solenoid shut-off valves 8 and 9 are attached is opened and connected to a tank 1, and a steam injection nozzle 3 is arranged at the front end of the liquid flow tube 2 so that it faces the inside of an intake tube 5 communicated to a cylinder. The first and second solenoid shut-off valves 8 and 9 are, controlled by a temperature detecting thermostat installed on an engine main body 7, an exhaust heat utilizing evaporating device 14 is attached to the liquid flow tube 2, and an off-time delay relay is connected to an engine start stop switch through a relay switch.