A focusing servo device, an optical disc recording/reproducing device and a focus-searching method are provided for making a focus of an energy beam emitted by a pick-up unit to fall in an accessible range of a data layer of a disc. The method comprises the following steps: recording the deviation of the focal point during each predetermined period when the focal point of the energy beam is fallen in the accessible range such that the optical disc recording/reproducing device is operated in a feedback control mode; determining a focus-searching range based on the recorded deviation of the focal point; and moving the focal point in the focus-searching range to make the focal point to fall in the accessible range when the focal point of the energy beam is fallen out of the accessible range such that the optical disc recording/reproducing device is operated in a focus-searching mode.