PURPOSE: To improve both an evaporation efficiency and a condensing efficiency by a method wherein some large projections are formed at an inner surface of a metallic pipe with a specified spacing therebetween and a pair of small projections are formed between the large projections and inclined toward the large projections.

CONSTITUTION: Tubular grooves 16 with their opening width W2 being less than a bottom width W1 are formed between adjoining large projections 12 and small projections 14. In the case where they are used as evaporating tubes, air bubbles are easily formed inside the tubular grooves 16, these air bubbles act as evaporation cores so as to promote evaporation of thermal medium liquid. Accordingly, it is possible to increase the gasification efficiency as compared with that of the heat transfer pipe in which uniform simple grooves are formed in the same pitch. In addition, the extremity ends of the large projections 12 are projected from the inner circumferential surface of a metallic pipe 10 rather than from the small projections 14 and the tubular grooves 16, so that in the case where they are used as a condensing pipe, separation of thermal medium liquid from the extremity ends of the large projections 12 is well performed and a liquid film is hardly formed on this part. Accordingly, there the ratio of exposure of a metallic surface at the extremity ends of the large projections 12 is high, no prohibition of heat exchanging operation between the metal and the thermal medium gas through the liquid film, resulting in that a high condensing efficiency can be attained.