Information recording/reproduction device and method

This information recording/reproduction device (101) records information onto or reproduces recorded information from a recording medium that has the following: a guide layer (12) that has a single-spiral guide track; and a plurality of recording layers (13). In said recording medium, a switchover region in which land tracks and group tracks switch comprises a first region in which pits and spaces having the same rotational-phase position are laid out radially in a periodic fashion with a first period and a second region in which pits and spaces having the same rotational-phase position are laid out radially in a periodic fashion with a second period. Both the first period and the second period are smaller than the spot diameter of a guide beam shone on the guide layer. This information recording/reproduction device is provided with a first-region detection means (540) that detects the first region, a second-region detection means (550) that detects the second region, and a switchover-region detection means (560) that detects the switchover region on the basis of the results of the first-region detection and/or the second-region detection.