This adhesive includes a copolymer that includes monomer units represented by (a-1), (a-2), (a-3), and (a-4) described below, and the following content is contained among all of the monomers which constitute the copolymer:(a-1) 5 to 45 wt % of an alkyl(meth)acrylate；(a-2) 0.01 to 10 wt % of a (meth)acrylate having a hydroxyl group or an allyl ether having a hydroxyl group；(a-3) 50 to 78 wt % of an alkoxyalkyl (meth)acrylate；(a-4) 1 to 25 wt % of an alkoxypolyalkylene glycol mono(meth)acrylate or an alkoxypolyalkylene glycol allyl ether.
