PURPOSE: To prevent freezing of the fluid in pipes and also drop of fluidity by heating the pipes through supply of the warm air from the engine room.

CONSTITUTION: During cruise in a cold district, the warm air from the engine room 4 is introduced into the enclosure 2 through a duct 5 with the aid of an exhaust fan 3. Thus the temperature in the enclosure 2 will not lower. Accordiingly freezing of the fluid in pipes included in the piping system 1 or drop of the fluidity of this fluid can be prevented.