Provided is a vacuum membrane distillation desalination device that is for a ship, is compact, and achieves high desalination efficiency. The vacuum membrane distillation desalination device (1) for a ship has: a vacuum distillation module (11) provided with a heating device (10), which heats seawater taken into the ship, a heated seawater duct (20), through which the seawater heated by the heating device (10) flows, a vacuum unit (21), a hydrophobic porous membrane (22), which separates the heated seawater duct (20) and the vacuum unit (21), and a cooling unit (23) which cools and condenses the vapor flowing into the vacuum unit (21) through the hydrophobic porous membrane (22) from the heated seawater of the heated seawater duct (20); and a water ejector (61) that is a decompression means that decompresses the vacuum unit (21). The heating device (10) heats seawater by means of heat from a heat source of the ship. The water ejector (61) decompresses the vacuum unit (21) to a pressure between the maximum vapor tension of water at the seawater temperature of the heated seawater duct (20) and 0.1 atm, inclusive.