Crude containing a comparatively large content of nickel, vanadium, or carbon residue is treated so as to supply a raw material to a downstream catalytic cracking process. A primary distillation tower fractionates first crude into a residue fraction partly used as raw oil of a catalytic cracking process and other fractions. A secondary distillation tower fractionates second crude containing a larger content of a catalytic poison with respect to catalysts used in the catalytic cracking process than the first crude into a light fraction included in a distillation temperature range of the other fractions and a heavy fraction as a rest thereof. A light fraction supply line supplies the light fraction to the primary distillation tower so as to be treated in the primary distillation tower.