An optical instrument comprising a plurality of focus drivers, including first and second focus drivers for respectively independently driving the first and second focus lenses within the plurality of focus lenses, and a second focus lens control position determination section for determining a control target position for every fixed period by referencing second focus position characteristic data that has been stored in the memory, based on control target position that has been determined by the first focus lens position determination section, wherein the plurality of focus drivers carryout driving of the first and second focus lenses based on control target positions for every fixed period that have been determined by the first and second focus lens control position determination sections.