A separation membrane having a hollow fiber shape for water treatment comprising, as a main component thereof, at least one compound selected from the group consisting of a polyamide, and a polyester, so that the total of contents of at least one compound selected from the group consisting of the polyamide, and the polyester is 70% by weight or more, wherein the separation membrane has, in an interior thereof in a longitudinal cross-section parallel to the thickness direction of the membrane and parallel to the lengthwise direction of a hollow fiber and also perpendicular to one surface of the membrane, a plurality of voids each having a depth (D 1) of 10 nm or more and 500 nm or less, a length (L 1) of 30 nm or more, and a ratio L 1 /D 1 of the length to the depth in a range of 2 or more, the depth (D 1) of the void referring to the length in the depth direction of the void in the case where the membrane thickness direction of the separation membrane is defined as the depth direction, the length (L 1) of the void referring to the length in the lengthwise direction of the void in the case where a direction at which a distance when two points on an edge of the void are joined is the longest is defined as the lengthwise direction of the void, and the depth (D 1) and the length (L 1) being determined by atomic force microscopy as described herein, and when a projected area of a cross-section of the separation membrane is defined as S 10, and an occupation area of the voids is defined as S 1, an occupancy rate of the voids in the cross-section, expressed by {(S 1 /S 10) × 100}, is 0.5% or more and 30% or less, wherein the occupancy rate is determined as described herein, the separation membrane has a thickness of 2 μm or more and 100 μm or less, and the separation membrane has a tensile elasticity of 1,000 to 6,500 MPa, determined in an environment of a temperature of 20°C and a humidity of 65%, using a tensile tester under conditions of a sample length of 100 mm and a tension rate of 100 mm/min. wherein the separation membrane has, in an interior thereof in a longitudinal cross-section parallel to the thickness direction of the membrane and parallel to the lengthwise direction of a hollow fiber and also perpendicular to one surface of the membrane, a plurality of voids each having a depth (D 1) of 10 nm or more and 500 nm or less, a length (L 1) of 30 nm or more, and a ratio L 1 /D 1 of the length to the depth in a range of 2 or more, the depth (D 1) of the void referring to the length in the depth direction of the void in the case where the membrane thickness direction of the separation membrane is defined as the depth direction, the length (L 1) of the void referring to the length in the lengthwise direction of the void in the case where a direction at which a distance when two points on an edge of the void are joined is the longest is defined as the lengthwise direction of the void, and the depth (D 1) and the length (L 1) being determined by atomic force microscopy as described herein, and when a projected area of a cross-section of the separation membrane is defined as S 10, and an occupation area of the voids is defined as S 1, an occupancy rate of the voids in the cross-section, expressed by {(S 1 /S 10) × 100}, is 0.5% or more and 30% or less, wherein the occupancy rate is determined as described herein, the separation membrane has a thickness of 2 μm or more and 100 μm or less, and the separation membrane has a tensile elasticity of 1,000 to 6,500 MPa, determined in an environment of a temperature of 20°C and a humidity of 65%, using a tensile tester under conditions of a sample length of 100 mm and a tension rate of 100 mm/min.