A heat transfer tube for a falling film type evaporator, in which water spreading characteristics, particularly the water spreading characteristics in the tube axis direction, enhancing the heat transfer ability. Three types of projections 2, 3, and 4 are formed on an external surface 1a of a heat transfer tube body 1. A respective plurality of projections 2 to 4 are arranged spirally in parallel to one another, forming projection groups 2a to 4a. The number of each projection group 2 to 4 is one. Pitches P2 to P4 for the projections 2 to 4 are in the range of 0.35 mm≦P4