PURPOSE: To obtain a spiral pervaporation membrane module capable of efficiently circulating a vapor without any pressure drop by specifying the physical values related to a gas flow resistance and dimensions such as thickness and length of the raw liq. spacer and permeated gas spacer.

CONSTITUTION: A flat pervaporation membrane having ≤41m2(STP)/m2.h.atm vapor permeation rate is formed into an envelope-shaped membrane leaf. One or more membrane leaves, a raw liq. spacer having 0.1-1.0mm length and in which the constants α and β defined by equation I (p is a pressure drop per cm distance, and (u) is the apparent linear velocity of pure water) are controlled respectively to ≤4×10-3 and to ≤2 in the case of pure water and a permeated gas spacer having ≥1.1mm thickness and ≤50cm effective length and in which the constants α' and β' defined by equation II (p' is a pressure drop per cm distance, and (u') is the linear velocity of a gas) are controlled respectively to ≤3×10-5 and to ≤2 in the case of air are wound on a gas collecting pipe, and the vapor efficiency of the module is adjusted to ≥60% when the vapor pressure on the supply side is controlled to 100-760mmHg and the permeated vapor pressure of the gas collecting pipe to 10-200mmHg.