PROBLEM TO BE SOLVED: To realize rapid autofocus in a rigid endoscope system. SOLUTION: A rigid endoscope system has a tube body, an objective lens, an eyepiece lens, an image sensor, a focus detection sensor, and a light beam emitted from the eyepiece in each direction of the image sensor and the focus detection sensor. A spectroscopic optical element that disperses to the eyepiece, a first optical system for forming an image of a part of the light beam emitted from the eyepiece on the image pickup sensor, and a part of the light beam emitted from the eyepiece on the focus detection sensor. It is provided with a second optical system for causing the focus to be adjusted, and a focus adjusting unit for adjusting the focus by moving the focus adjusting lens included in the first optical system in the optical axis direction based on the detection signal. The total F value up to the system is configured to be smaller than the total F value from the objective lens to the first optical system. [Selection diagram] Fig. 1【課題】硬性内視鏡システムにおいて迅速なオートフォーカスを実現する。【解決手段】硬性内視鏡システムは、管体と、対物レンズと、接眼レンズと、撮像センサと、焦点検出センサと、接眼レンズから射出される光束を撮像センサと焦点検出センサのそれぞれの方向へ分光する分光光学素子と、接眼レンズから射出された一部の光束を撮像センサへ結像させるための第１光学系と、接眼レンズから射出された一部の光束を焦点検出センサへ結像させるための第２光学系と、検出信号に基づいて第１光学系に含まれる焦点調整レンズを光軸方向へ移動させることにより焦点調整を行う焦点調整部とを備え、対物レンズから第２光学系までの全体のＦ値は、対物レンズから第１光学系までの全体のＦ値よりも小さくなるように構成されている。【選択図】図１
