Information recording and reproducing device

An information recording/reproducing apparatus for performing recording or reproducing of information by applying an evanescent light onto a recording medium, said information recording/reproducing apparatus comprising:

• a light source for emitting a laser beam corresponding to the recording or the reproduction;
• an optical system for leading the emitted laser beam onto the recording medium;
• a diffracting device, disposed on an optical path of the laser beam in said optical system, for diffracting the led laser beam to be separated into a main beam and a sub beam;
• an evanescent light generating device for (i) applying an evanescent light associated with the main beam onto a track, where a recording pit is formed, of a plurality of tracks disposed at a recording surface of the recording medium, and (ii) applying an evanescent light associated with the separated sub beam onto a track, which is disposed at the recording surface and where a recording pit is not formed;
• a sub light receiving device for receiving a return light associated with the sub beam;
• a main light receiving device for receiving a return light associated with the main beam;
• a displacing device for displacing said evanescent light generating device in such a direction as to change a gap between the recording surface and said evanescent light generating device;
• and
• a controlling device for controlling said displacing device in such a manner that the gap can have a predetermined target value, on the basis of a gap error signal which is provided with a light amount of the received return light associated with the sub beam and a light amount of the received return light associated with the main beam.