Abstract: In an inner surface-grooved heat transfer tube, a plurality of fins is formed on the inner surface thereof along a line forming a first predetermined angle with respect to the longitudinal axis of the tube, a plurality of notches is defined on the fins along a line forming a second predetermined angle with respect to the longitudinal axis, and the depth Hf' of the notches is specified to be 20% or more and below 40% (0.2.ltoreq.Hf'/Hf<0.4) with respect to the height Hf of the fins, to provide an inner surface-grooved heat transfer tube which can suppress pressure loss of a refrigerant, and by which improvements in performance of condensation and evaporation are intended. In addition no increase of power consumption is required for the pump.