The present invention provides an adhesive capable of affording an adhesive layer showing reduced stickiness, reduced cohesive failure and the like. An adhesive containing a copolymer obtained by copolymerizing monomers containing a (meth)acrylic acid alkyl ester as a main component, and a vinyl monomer having a hydroxyl group and/or a carboxyl group and which has an average molecular radius of not less than 70 nm as measured by a multi angle laser light scattering method.