Provided is a paper machine contamination preventive agent that has high fixability to rolls and the like of a paper machine, that positively finds a silicone oil capable of imparting releaseability and water-repellent properties to the rolls or the like immediately upon being supplied to the rolls or the like, and that uses the silicone oil as a main component. Further provided is a paper machine contamination preventive agent using a silicone oil that permits transfer of less foreign matters from a wet paper web than that in a case where a contamination preventive agent containing a dimethylpolysiloxane base oil is a main component. The paper machine contamination preventive agent is fed to a paper machine and has a sidechain-type modified silicone oil or a sidechain both-termini modification silicone oil as a main component.