The endoscope apparatus includes an optical system 240 including a focus lens 220, a connection unit 260 to which an interchangeable optical system is connected, an image sensor 250 that outputs a captured image based on the optical system 240 and the interchangeable optical system 100, and the like. The focus control unit 210 includes a focus control unit 210 that controls the focus lens 220 based on step amount information that represents the control amount of the focus lens 220, and a processing unit 300. The processing unit 300 determines whether the interchangeable optical system is known or unknown. If it is determined that the interchangeable optical system is known, a first step amount determination process is performed. If it is determined that the interchangeable optical system is unknown, a second step amount determination process is performed. Do.内視鏡装置は、フォーカスレンズ２２０を含む光学系２４０と、交換式光学系が接続される接続部２６０と、光学系２４０と交換式光学系１００に基づいて撮像画像を出力する撮像素子２５０と、フォーカスレンズ２２０の制御量を表すステップ量情報に基づいて、フォーカスレンズ２２０の制御を行うフォーカス制御部２１０と、処理部３００を含み、処理部３００は、交換式光学系が既知か未知かの判定処理を行い、交換式光学系が既知であると判定された場合には、第１のステップ量決定処理を行い、未知であると判定された場合には、第２のステップ量決定処理を行う。
