PURPOSE: To provide a dry evaporator with good efficiency in heat-exchanging performance available at a low cost by using cooling tubes which function at an optimal heat-transfer rate in dealing with the changes in state of the refrigerant flowing through a refrigerant circuit.

CONSTITUTION: A channel for refrigerant passed through a shell 1 is formed of a ripple-finned tube 5, which has spiral groove 52 cut inside, on the side of the inlet and of an inner-finned tube 6, which is provided with inner fins 62 inside, on the side of the outlet. In the region where the refrigerant becomes a slag flow and a vapor flow in the form of rings, the groove 52 accelerates the boiling of the refrigerant and collects the atomized particles that the boiling produces in the vapor flow so that the overall heat-transmission coefficient is improved. In the region where the refrigerant dries out and turns from a vapor flow to a single-phase vapor flow, that is, on the side of the outlet of the refrigerant channel, the refrigerant undergoes exchange of heat with liquid to be cooled through the inner-finned tube 6 whose area effective for the exchange of heat per unit length is large. Thus by putting a ripple- finned tube 5 and an inner-finned tube 6 to effective use in heat-transfer rate on the side of refrigerant a dry evaporator can be made available at a low cost relative to improvement in the heat-exchange efficiency.