A separation membrane comprising: a supporting membrane; and a separation functional layer formed on the supporting membrane, wherein the separation functional layer comprises a polymerized product of a polyfunctional amine with a polyfunctional acid halide, the polyfunctional amine comprises a polyfunctional aliphatic amine as a main component, the separation functional layer has a hollow protuberant structure, that is a hollow structure which is observed in an image obtained by examining a cross-section of the separation functional layer with a transmission electron microscope, and in which a ratio of (protuberance height of the separation functional layer)/(thin-membrane thickness of the separation functional layer) is larger than 1.1, wherein the ratio of (protuberance height of the separation functional layer)/(thin-membrane thickness of the separation functional layer) is determined as set out in the description, and the separation functional layer has a relative surface area of 1.5-10.0, wherein the relative surface area is determined as set out in the description, wherein the relative surface area is the ratio of the surface area of the separation functional layer to the surface area of the porous supporting layer, wherein the protuberant structure has an average number density of protuberances of 5-300 protuberances per μm 2 determined as described in the specification, and wherein in the separation functional layer, the presence ratio in which the amino groups and amide groups that are derived from the polyfunctional aliphatic amine and the carboxy groups and amide groups that are derived from the polyfunctional acid halide are present [(amino groups + amide groups)/(carboxy groups + amide groups)] satisfies the following expression: 0.8 ≤ (number of moles of amino groups and amide groups derived from polyfunctional aliphatic amine)/(number of moles of carboxy groups and amide groups derived from polyfunctional acid halide) ≤ 1.2 wherein the polyfunctional aliphatic amine has a logP of -1.0 to 0.0 with logP being the common logarithm of octanol-water distribution coefficient determined according to JIS Z 7260-107; and wherein the polyfunctional aliphatic amine is a piperazine compound selected from the group consisting of 2,5-dimethylpiperazine, 2-methylpiperazine, 2-ethylpiperazine, 2,5-diethylpiperazine, and mixtures of two or more thereof. a supporting membrane; and a separation functional layer formed on the supporting membrane, wherein the separation functional layer comprises a polymerized product of a polyfunctional amine with a polyfunctional acid halide, the polyfunctional amine comprises a polyfunctional aliphatic amine as a main component, the separation functional layer has a hollow protuberant structure, that is a hollow structure which is observed in an image obtained by examining a cross-section of the separation functional layer with a transmission electron microscope, and in which a ratio of (protuberance height of the separation functional layer)/(thin-membrane thickness of the separation functional layer) is larger than 1.1, wherein the ratio of (protuberance height of the separation functional layer)/(thin-membrane thickness of the separation functional layer) is determined as set out in the description, and the separation functional layer has a relative surface area of 1.5-10.0, wherein the relative surface area is determined as set out in the description, wherein the relative surface area is the ratio of the surface area of the separation functional layer to the surface area of the porous supporting layer, wherein the protuberant structure has an average number density of protuberances of 5-300 protuberances per μm 2 determined as described in the specification, and wherein in the separation functional layer, the presence ratio in which the amino groups and amide groups that are derived from the polyfunctional aliphatic amine and the carboxy groups and amide groups that are derived from the polyfunctional acid halide are present [(amino groups + amide groups)/(carboxy groups + amide groups)] satisfies the following expression: 0.8 ≤ (number of moles of amino groups and amide groups derived from polyfunctional aliphatic amine)/(number of moles of carboxy groups and amide groups derived from polyfunctional acid halide) ≤ 1.2 wherein the polyfunctional aliphatic amine has a logP of -1.0 to 0.0 with logP being the common logarithm of octanol-water distribution coefficient determined according to JIS Z 7260-107; and wherein the polyfunctional aliphatic amine is a piperazine compound selected from the group consisting of 2,5-dimethylpiperazine, 2-methylpiperazine, 2-ethylpiperazine, 2,5-diethylpiperazine, and mixtures of two or more thereof.