An observation optical system according to the present invention guides an observation light beam from a living body. An imaging element, upon receipt of the observation light beam guided by the observation optical system, captures an observation image of the living body. An observation focus adjustment unit is disposed on a light path of the observation light beam in the observation optical system, and adjusts the focus of the observation optical system. A detection means detects at least any one of a user's gaze direction, speech uttered by the user, and the user's gestures. A control unit drives the observation focus adjustment unit on the basis of a result of detection by the detection means so as to adjust focus on the area of attention in the observation image (S4-S11).