The present invention relates to a film base material for an adhesive skin patch, which includes an elastomer film unevenly having unevenness on at least one surface thereof, in which, in one unevenness in which the distance perpendicular to the surface of the elastomer film between the top of the unevenness and the bottom thereof is the longest among the plurality of unevenness, the distance is within the range of from 1 to 5 μm; in another unevenness in which the distance perpendicular to the surface of the elastomer film between the top of the unevenness and the bottom thereof is the shortest among the plurality of unevenness, the distance is within the range of from 0.1 to 0.9 μm; and the 10-point average roughness of the surface is within the range of from 0.5 μm to 3 μm, and which is decreased in glossy texture on the surface thereof and inconspicuous when it is applied to the skin or the like; and the adhesive skin patch including the film base material.