{HEAD ~ an irradiation beam photo detector} for producing {TAIL ~ an amount} of irradiation beam detection signal according to the amount of a laser beam irradiated from said laser beam source onto an optical disk; and 
for producing
{ HEAD ~ an irradiation beam photo detector } for producing { TAIL ~ an amount } of irradiation beam detection signal according to the amount of a laser beam irradiated from said laser beam source onto an optical disk ; and
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL 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