A wet laid nonwoven fabric containing organic synthetic fibers as a primary component with one surface and another surface, the nonwoven fabric obtained by hot pressing a single layer structure, wherein the one surface is configured for coating a semipermeable membrane thereon, while the other surface is a non-coated surface, when a region extending from the one surface of the nonwoven fabric to a predetermined portion in the thickness direction is designated as a coated layer region, a region extending from the other surface of the nonwoven fabric to a predetermined portion in the thickness direction is designated as a non-coated layer region, a region between the coated layer region and the non-coated layer region is designated as a middle layer region, a basis weight of the coated layer region is designated as E, a basis weight of the non-coated layer region is designated as I, a basis weight of the middle layer region is designated as K and a basis weight of the nonwoven fabric is designated as B, equations (a), (b), and (c) are satisfied, when a pressure drop of the nonwoven fabric is designated as A, a pressure drop of the coated layer region is designated as C, a pressure drop of the non-coated layer region is designated as G and a pressure drop of the middle layer region is designated as H, equations (d), (e), and (f) are satisfied,, the degree of thermal melting of the organic synthetic fibers in the middle layer region is lower than the degree of thermal melting of the organic synthetic fibers in the coated layer region and the non-coated layer region, and any one surface of the nonwoven fabric may serve as the one surface, whereby the basis weight measurement of the nonwoven fabric is carried out according to JIS P 8124:1998 "Paper and board - Determination of grammage", and corresponding values for A, C, E, G, H, I and K are determined according to the description. 22.5 % ≤ E / B × 100 ≤ 27.5 % 22.5 % ≤ I / B × 100 ≤ 27.5 % B = E + K + I H / K < C / E H / K < G / I 10 % ≤ H/K / A/B × 100 ≤ 70 % the one surface is configured for coating a semipermeable membrane thereon, while the other surface is a non-coated surface, when a region extending from the one surface of the nonwoven fabric to a predetermined portion in the thickness direction is designated as a coated layer region, a region extending from the other surface of the nonwoven fabric to a predetermined portion in the thickness direction is designated as a non-coated layer region, a region between the coated layer region and the non-coated layer region is designated as a middle layer region, a basis weight of the coated layer region is designated as E, a basis weight of the non-coated layer region is designated as I, a basis weight of the middle layer region is designated as K and a basis weight of the nonwoven fabric is designated as B, equations (a), (b), and (c) are satisfied, when a pressure drop of the nonwoven fabric is designated as A, a pressure drop of the coated layer region is designated as C, a pressure drop of the non-coated layer region is designated as G and a pressure drop of the middle layer region is designated as H, equations (d), (e), and (f) are satisfied,, the degree of thermal melting of the organic synthetic fibers in the middle layer region is lower than the degree of thermal melting of the organic synthetic fibers in the coated layer region and the non-coated layer region, and any one surface of the nonwoven fabric may serve as the one surface, whereby the basis weight measurement of the nonwoven fabric is carried out according to JIS P 8124:1998 "Paper and board - Determination of grammage", and corresponding values for A, C, E, G, H, I and K are determined according to the description. 22.5 % ≤ E / B × 100 ≤ 27.5 % 22.5 % ≤ I / B × 100 ≤ 27.5 % B = E + K + I H / K < C / E H / K < G / I 10 % ≤ H/K / A/B × 100 ≤ 70 %