An apparatus for preparing electrophotographic photosensitive members comprises a means for forming a charge generation layer by coating a charge generation layer coating solution containing two or more kinds of charge-generating materials having different maximum absorption wavelengths, wherein the apparatus further comprises a means for measuring absorbance or transmittance at the respective maximum absorption wavelengths of said coating solution to measure the mixing ratio of the respective charge-generating materials, and a means for controlling the mixing ratio by controlling the feed amount of the respective charge-generating materials.