A release agent applicator for use with a copying machine providing even application of the release agent to a fixing roll of a plain paper copying machine with little leakage of the release agent. A porous polyethylene tetrafluoride resin tube is accommodated in a divided-type support composed of two members which, when joined together, form a longitudinally extending opening having a width smaller than the maximum width of a cavity formed inside the support. The major portion of the outer surface of the porous resin tube is in contact with abutting walls of the cavity to be sealed thereby, and the remaining portion of the tube surface extends outwardly through the support opening to provide a release agent outlet. Both the porous tube and the support may be provided with air inlets having the diameter greater than the diameters of the pores in the porous tube to introduce air into the interior of the porous tube. Further, the porous tube may be initially covered with a film of a polymer having a low melting point. When the applicator is used for the first time, the normal heating of the fixing roll melts the polymer and readies the tube for use.