PURPOSE: To separate waste mash liquid into alcohol and purified water, by separating it into a solid component and a liquid component and subjecting the liquid component to reverse osmosis with a semipermeable membrane.

CONSTITUTION: Waste mash liquid is stored in an evaporation tank 36 and hot waste water is circulated through a heating pipe 50 provided in the evaporation tank 36 to heat the inside thereof. The inside of a distillate tank 40 is decompressed by actuating a vacuum pump 58 and decompressing the distillate tank 40. In this state, waste mash liquid is sent under pressure into the tank 36 via a transport pipe 44 with a pump 46 and dispersed. Waste mash liquid introduced into the tank 36 is boiled and evaporated and a liquid component is gasified and vapor is passed through a communication pipe 48 and introduced into a cooler 38 and also a solid component in a dry state remains and deposits on the bottom of the tank 36. The vapor introduced into the cooler 38 is cooled with a cooling pipe 52 and liquefied. This is fed to a semipermeable membrane module device 42 and separated.