To provide a pressure-sensitive adhesive composition for forming a pressure-sensitive adhesive layer that can maintain high initial adhesive force and adhesion reliability (particularly, repelling resistance) upon bonding and can easily be peeled off and can easily separate and dismantle a joined part upon peeling from an adherend.

The invention relates to a pressure-sensitive adhesive composition comprising: a monomer mixture comprising the following (a1), (a2) and (a3) or partially polymerized product thereof, and thermal-expandable fine particles: (a1): alkyl(meth)acrylate monomer having 4 to 12 carbon atoms in its alkyl moiety and having a glass transition temperature when formed into a homopolymer of lower than 0°C; (a2): monomer having at least one nitrogen atom and one ethylenically unsaturated bond in its molecule; and (a3): monomer having one ethylenically unsaturated bond in its molecule and having a glass transition temperature when formed into a homopolymer of 0°C or higher (excluding (a2) above).