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