Focus servo control device, and information recording/reproducing device using the same

A recording/reproducing device for recording information in a recording medium having a guide layer and a plurality of recording/reproducing layers, or reproducing the information from the recording medium, comprising:

• an objective lens:
• a first detector configured to detect a first focus error signal based on a reflected light reflected when the guide layer is irradiated with a first laser for focus servo through the objective lens;
• a first controller configured to control the objective lens based on the first focus error signal, so that a focal point of the first laser agrees with the guide layer;
• a second detector configured to detect a second focus error signal based on a reflected light reflected when the recording layer is irradiated with a second laser for recording/reproducing through the objective lens;
• a second controller configured to change a relative distance between the focal point of the second laser and the focal point of the first laser based on the second focus error signal, so that the focal point of the second laser agrees with a target recording/reproducing layer in the plurality of recording/reproducing layers;
• and
• a switcher configured to switch the first focus error signal and the second focus error signal mutually between each other at a timing when the focal point of the first laser substantially agrees with the guide layer and the focal point of the second laser substantially agrees with the target recording/reproducing layer, so that the first focus error signal is input to the second controller and the second focus error signal is input to the first controller,
• wherein after the first focus error signal and the second focus error signal are switched, the first controller controls the focal point of the second laser based on the second focus error signal, so that the focal point of the second laser agrees with the target recording/reproducing layer in the recording/reproducing layers.