An anodized layer formation method of at least one example embodiment of the present invention includes the steps of: (a) providing an aluminum base which has a machined surface; (b) forming, in the surface of the aluminum base, a minute uneven structure which has a smaller average neighboring distance than an average neighboring distance of a plurality of minute recessed portions that an intended porous alumina layer has; and (c) after step (b), anodizing the surface of the aluminum base, thereby forming a porous alumina layer which has the plurality of minute recessed portions. According to at least one embodiment the present invention, a porous alumina layer which has uniformly-distributed minute recessed portions can be formed over a machined surface of an aluminum base.