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