An aim of the invention is to provide a ply adhesive that is capable of expressing a sufficient ply adhesion strength, does not harden an area where the ply adhesive is applied, and does not worsen paper texture. [Solution] The problem can be solved by a ply adhesive that comprises: 1-5 mass% of carboxymethylcellulose, a 1 mass% aqueous solution of said carboxymethylcellulose having a viscosity of 100 mPa.s or lower, as an adhesive; and 1-5 mass% of at least one member selected from among propylene glycol, glycerol and butylene glycol as a softening agent.