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