An information recording/reproducing device diffracts laser light into main- and sub-beams, irradiates evanescent light in relation to the main beam by an evanescent light generating element to a track where a recording pit provided on a recording surface of a recording medium is formed and evanescent light in relation to the sub-beam to be separated to a track where no recording pit provided on the recording surface of the recording medium is formed. A moving element moves the evanescent light generating element to change a gap with the recording surface. Return light in relation to the sub- and main-beam are received by sub- and main-light receiving elements, respectively. A control element controls the moving element so as to make the gap become a predetermined target value in accordance with a gap error signal containing a signal indicative of an amount of the return light in relation to the received sub-beam.