A fastener member, comprising a base material made of a copper alloy containing zinc at a concentration of 30% by mass or more and 43% by mass or less, and a black copper oxide coating covering at least a part of the base material, characterized in that when the black copper oxide coating is divided into a lower layer below a center of thickness and an upper layer above the center of thickness, the porosity in % of the lower layer is smaller than that of the upper layer, and a difference between the porosity of the lower layer and that of the upper layer is 10% or more, wherein the porosity in % is measured according to a following method in which: - a cross section in a direction perpendicular to a surface of the black copper oxide coating is cut out from the fastener member as an object of measurement, and the cross-section of the black copper oxide coating including a boundary with the base material is observed with a scanning electron microscope at a magnification of 50 000, - on the SEM photograph, the highest brightness portion is defined as the brightness 255, the lowest brightness portion is defined as the brightness 0, and binarization to black and white is made with the boundary at brightness 128, - the number of black and white pixels in the binarized image is measured in the upper and lower layers, respectively, and the ratio of the number of black pixels to the total number of pixels is calculated for the upper layer and the lower layer, respectively, and thus defined as the porosity of the upper layer and the lower layer, respectively, - the porosity is determined for 10 or more arbitrary fields of view, and the average value thereof is defined as the measured value. characterized in that when the black copper oxide coating is divided into a lower layer below a center of thickness and an upper layer above the center of thickness, the porosity in % of the lower layer is smaller than that of the upper layer, and a difference between the porosity of the lower layer and that of the upper layer is 10% or more, wherein the porosity in % is measured according to a following method in which: - a cross section in a direction perpendicular to a surface of the black copper oxide coating is cut out from the fastener member as an object of measurement, and the cross-section of the black copper oxide coating including a boundary with the base material is observed with a scanning electron microscope at a magnification of 50 000, - on the SEM photograph, the highest brightness portion is defined as the brightness 255, the lowest brightness portion is defined as the brightness 0, and binarization to black and white is made with the boundary at brightness 128, - the number of black and white pixels in the binarized image is measured in the upper and lower layers, respectively, and the ratio of the number of black pixels to the total number of pixels is calculated for the upper layer and the lower layer, respectively, and thus defined as the porosity of the upper layer and the lower layer, respectively, - the porosity is determined for 10 or more arbitrary fields of view, and the average value thereof is defined as the measured value. - a cross section in a direction perpendicular to a surface of the black copper oxide coating is cut out from the fastener member as an object of measurement, and the cross-section of the black copper oxide coating including a boundary with the base material is observed with a scanning electron microscope at a magnification of 50 000, - on the SEM photograph, the highest brightness portion is defined as the brightness 255, the lowest brightness portion is defined as the brightness 0, and binarization to black and white is made with the boundary at brightness 128, - the number of black and white pixels in the binarized image is measured in the upper and lower layers, respectively, and the ratio of the number of black pixels to the total number of pixels is calculated for the upper layer and the lower layer, respectively, and thus defined as the porosity of the upper layer and the lower layer, respectively, - the porosity is determined for 10 or more arbitrary fields of view, and the average value thereof is defined as the measured value.