An automatic processing method by developing a plural number of exposed photosensitive lithographic printing plates with a developer, which comprises the previously calculating step, the measuring step and the replenishing step as defined herein, wherein during a period from immediately after start of operation of an automatic processing apparatus until the measured electric conductivity value of the developer exceeds the target electric conductivity value, the target electric conductivity value is corrected using a first operation expression as previously defined for every replenishment of the developer replenisher; and after the measured electric conductivity value of the developer first exceeds the target electric conductivity value after start of operation of the automatic processing apparatus, the target electric conductivity value is corrected using a second operation expression for every replenishment of the developer replenisher.