Abstract: There is provided a fluororesin which has a low friction coefficient, superior wear resistance and a superior friction characteristic in the presence of a lubricating oil and/or an operating oil. The fluororesin has a structure in which some of the hydrogen atoms and/or fluorine atoms bonded to carbon atoms of a main frame resin are substituted with an oxygen-containing functional group. Visible light transmittance in a wavelength of 600 nm is increased as compared with that of the main frame resin. There is also provided a method of reforming a fluororesin, comprising extracting some of the hydrogen atoms and/or fluorine atoms bonded to carbon atoms of a main frame resin to introduce an unsaturated bond; and applying dissociation energy of the unsaturated bond in the presence of oxygen. There are further provided a sliding member, a sliding apparatus and a sliding system.