In order to reduce the burden on the surgeon by preventing sufficiently miniaturizing the mirror body while obtaining a stereoscopic image from two directions and preventing it from interfering with surgical operation and monitor observation, A first imaging optical system for acquiring optical images of a pair of subjects having parallax through a pair of openings arranged in parallel from a first observation direction, and a second imaging optical system having another pair of openings arranged in parallel And a second imaging optical system that acquires an optical image of another pair of subjects having parallax through the second observation direction different in angle around the optical axis from the first observation direction, An arrangement is made such that the area of the opening portion of the first imaging optical system is larger than the area of the opening portion of the second imaging optical system and the first imaging optical system and the second imaging optical system satisfy the following conditional expression Has been done. 0.4 L 2 / L 1 0.6 (1) Here, L1 is the distance between the centers of the openings of the first imaging optical system, and L2 is the distance between the centers of the openings of the second imaging optical system.2方向から立体画像を取得しながら鏡体を十分に小型化し、手術作業やモニタ観察の妨げとなることを防止して、術者の負担を軽減することを目的として、手術用観察システムは、並列に配置された1対の開口部を介して視差を有する1対の被写体の光学像を第1の観察方向から取得する第1撮像光学系と、並列に配置された他の1対の開口部を介して視差を有する他の1対の被写体の光学像を、第1の観察方向とは光軸回りの角度が異なる第2の観察方向から取得する第2撮像光学系と、を備え、第1撮像光学系の開口部の面積が第2撮像光学系の開口部の面積よりも大きく、かつ、第1撮像光学系と第2撮像光学系とが以下の条件式を満足するように配置されている。 0.4≦L2/L1≦0.6・・・ (1) ただし、L1は第1撮像光学系の開口部の中心間の距離であり、L2は第2撮像光学系の開口部の中心間の距離である。
