A pressure-sensitive adhesive composition containing an acrylic copolymer (A) having a structural unit (a1) derived from an alkyl (meth)acrylate (a1)′ and a structural unit (a2) derived from a functional group-containing monomer (a2)′, a crosslinking agent (B), and a photochromic dye (C) selected from a group consisting of dithienylethene-based compounds, oxazine-based compounds and naphthopyran-based compounds has a relatively rapid rate of color change from colored to colorless after termination of irradiation with UV rays, has excellent photochromic performance and can be a pressure-sensitive adhesive layer of a colorless pressure-sensitive adhesive sheet.