To provide a stain-proofing agent for a paper machine, effectively preventing, by a simple method, stain in dry part areas, at least the surface of cylindrical dryers even when no spray space is in the paper machine.

The stain proofing agent is applied to a method for stain-proofing and for preventing stain of a contact part by continuously supplying, so as to prevent stain of the contact parts in the dry part D of a paper machine, the agent being applied to a paper W in a state before its coming in into the dry part. The stain proofing agent is obtained by emulsifying wax, mineral oil, vegetable oil, animal oil or synthetic oil with a surfactant.