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