PURPOSE: To remove the generation of shift between a main beam and a subbeam at the time of accessing a track by executing track access and test seaking by the main beam and finding out the initial value of a servo necessary for the track movement of the sub-beam during the operation of the device.

CONSTITUTION: The 1st beam photodetector 21 receives light from an optical disk 1 of the 1st beam to obtain the 1st photodetecting signal and the 2nd beam photodetector 22 receives light from an optical storage medium 1 of the 2nd beam to obtain the 2nd photodetecting signal. Driving information obtained when the 2nd beam moves on a track is found out by the 2nd beam movement driving amount measuring means 500. Since the 2nd beam is moved on the track based upon the driving information, the 1st and 2nd beams can access the same track.