An apparatus for fixing a toner image by transporting a toner image bearing material as it is held between a fixing roll and a compression roll. In the apparatus, which is positioned above the fixing roll, a release agent having a viscosity of 50 to 100,000 cS is applied onto the surface of the fixing roll through a porous fluorocarbon resin membrane having a pore size of 0.01 to 10 .mu.m, a porosity of 35 to 85%, and a thickness of 50 .mu.m to 1 mm. The porous membrane may be located on the inner surface of the bottom of a tank containing the release agent above an opening in the tank bottom.