To provide a polyurethane adhesive in which the adhered part is flexible and the adhesion can be performed in a short time and which causes no problem of pot life, and an adhering method of a polyurethane foam.

The polyurethane adhesive is an adhesive comprising a polyol, a polyisocyanate and a catalyst in which the polyisocynate includes a polymethylenepolyphenylpolyisocyanate and the catalyst includes a thermosensitive catalyst, and this adhering method includes: applying the polyurethane adhesive containing a water content of 0.005 to 0.5 mass% to a surface of a polyurethane foam to be adhered; superimposing an object to be adhered to the polyuretane foam on the surface of the polyurethane foam to be adhered; and irradiating the polyurethane foam and the object to be adhered with a microwave.