An object of the invention is to eliminate the disposition change of {HEAD ~ plural beam spots} on {TAIL ~ the inner face} of a drum 
on
An object of the invention is to eliminate the disposition change of { HEAD ~ plural beam spots } on { TAIL ~ the inner face } of a drum
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH