PURPOSE: To obtain the titled desalinator which contrives energy saving, by providing an ejector-driving water pipe branched from a drain pipe for sea water and connected to an ejector, an ejector pump, a supplemental water pipe for distillation connected to a condenser, etc.

CONSTITUTION: Cooling sea water which has been sucked through an intake opening 52 for sea water at the hull and pressurized by a pump 52 is supplied through a supply pipe 64 to a cooling pipe 57. The sea water which has carried out cooling action is discharged through a drain pipe 60 for sea water, but its part is pressurized by an ejector pump 54 and supplied as ejector-driving water through an ejector-driving water pipe 59 to an ejector 55. On the other hand, supplemental water for distillation is supplied through a supplementary water pipe 63 for distillation to the lower part of a condenser 51. Steam from sea water evaporated at a heating part 65 is cooled and condensed by the cooling pipe 57, and distilled water reserved as condensed water in a saucer 66 is transferred through a pump 67 to a tank 58 for limpid water.