PURPOSE: To obtain a heat transfer tube of superior boiling and condensing performance by forming projections with acute-angled tips and divergent recesses having very small openings between their roots on the heat transfer wall surface of a heat transfer tube used for a heat exchanger which is used both for a condenser and an evaporator.

CONSTITUTION: When a heat exchanger is used as a condenser flowing a condensing refrigerant outside a tube and cooling water inside the tube, since projections 3 with acute-angled tips 3a are formed on a heat transfer wall surface 2, the liquid film of the refrigerant liquid condensed by cooling water in the tube become very thin at the tips 3a by surface tension and condensing performance is improved. When used as an evaporator to the contrary, divergent recesses 4 formed on the heat transfer wall surface 2 become nuclei for the boiling bubbles of the refrigerant liquid and accelerate boiling. Therefore, boiling performance is improved. By so doing, a heat transfer tube of superior performance both for condenser and evaporator use can be obtained.