The adhesive according to the present invention includes: a modified olefin polymer (A) in which a polymer of a C 2 -C 20 n α -olefin including structural units derived from a C 4 -C 20 n α -olefin is modified by a monomer having a functional group capable of reacting with an isocyanate group, and which has a heat of fusion of 0 J/g to 50 J/g as measured in accordance with JIS K7122; and a polyisocyanate (B).