This adhesive includes a copolymer that includes monomer units represented by (a-1), (a-2), (a-3), and (a-4) described below, and is characterized by containing the content described below among all of the monomers which constitute the copolymer. (a-1) Alkyl(meth)acrylate 5-45 wt% (a-2) (meth)acrylate having a hydroxyl group or an allyl ether having a hydroxyl group 0.01-10 wt% (a-3) Alkoxyalkyl(meth)acrylate 50-78 wt% (a-4) Alkoxy polyalkylene glycol mono(meth)acrylate or alkoxy polyalkylene glycol allyl ether 1-25 wt%一種黏著劑，包含共聚物而成，上述共聚物包含下述（a－1）、（a－2）、（a－3）及（a－4）所示的單體單元，該黏著劑的特徵在於：在構成共聚物的全部單體中包含下述含量而成。（a－1）5重量%～45重量%的（甲基）丙烯酸烷基酯；（a－2）0.01重量%～10重量%的具有羥基的（甲基）丙烯酸酯或具有羥基的烯丙醚；（a－3）50重量%～78重量%的（甲基）丙烯酸烷氧基烷基酯；以及（a－4）1重量%～25重量%的烷氧基聚亞烷基二醇單（甲基）丙烯酸酯或烷氧基聚亞烷基二醇烯丙醚。
