To provide a method and apparatus for parting a glass rod without causing a crack or rupture at a grasped root portion of the glass rod in parting the glass rod for producing a glass preform. The first and second lens groups are installed in first and second single bodies, which are coupled to a third single body having the reflection mirror to reflect the image incident from the first single body to the second single body. The voltage applied by the first charging member is decreased such that the surface potential of the image carrier after the voltage is applied by the first charging member is decreased as the film on the image carrier becomes thinner.