An adhesive includes a modified olefin polymer (A) allowing a polymer of a C2 to C20 ±-olefin having a structural unit derived from a C4 to C20 ±-olefin to be modified with a monomer having a functional group capable of reacting with an isocyanate group and having a heat of fusion measured in accordance with JIS K7122 of 0 J/g or more and 50 J/g or less and a polyisocyanate (B).