This invention relates to a recording/reproducing optical disk device for recording data on various types of optical disks and reproducing data recorded on the optical disks and a reproduction-only (read-only) optical disk device for reproducing data recorded on various types of optical disks. 
Conventionally, an optical disk device for recording data on an optical disk having recording tracks by use of laser light output from a semiconductor laser oscillator mounted on an optical head or reproducing data recorded on the optical disk is put into practical use. 
In the above optical device, at most two types of optical disks can be dealt with in the prior art and the types of the optical disks are determined by using an additional sensor which detects the presence or absence of a cartridge, which loads the optical disk or an ID hole formed in the cartridge. 
If the number of optical disk types used increase, they cannot be correctly identified by the prior art method or, if they can, the cost becomes prohibitively high, because the number of ID hole sensors increases.  Further, in a case where the optical disk, originally loaded into the cartridge and is subsequently removed, determination of the optical disk cannot be made accurately.  If the determination is erroneous, there occurs the possibility that power, much greater than the optimum tolerable power of each optical disk is applied to the optical disk, resulting in the desctruction of information data, particularly in the case of a recording optical disk.