{HEAD ~ a defect detection circuit} configured to compare sad amount of irradiation beam detection signal with a reference voltage and maintain a substantially constant output voltage to said drive circuit during a first period of {TAIL ~ time}, 
{ HEAD ~ a defect detection circuit } configured to compare sad amount of irradiation beam detection signal with a reference voltage and maintain a substantially constant output voltage to said drive circuit during a first period of { TAIL ~ time } ,
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH