The imaging unit 30 includes a focus switching type observation optical system 33 including fixed lenses 56 a and 56 b and a moving lens 66, fixed frames 55 and 57 for holding the fixed lenses 56 a and 56 b, a photographing optical axis of the observation optical system 33 O, a movable frame 65 which is movable so as to be able to advance and retract in a direction along the direction O, and which is fixed in the fixed frames 55, 57, accommodates the moving frame 65 so as to freely advance and retreat, 65 and a correction frame 47 which is provided with a stopper 60 for regulating the movement of the photographing optical axis O in one direction by abutment with the correction frame 47 and which can be fine-adjusted freely so as to realize one focal length of the observation optical system 33 .撮像ユニット30は、固定レンズ56a,56bと移動レンズ66とを含む焦点切替方式の観察光学系33と、固定レンズ56a,56bを保持する固定枠55,57と、観察光学系33の撮影光軸Oに沿った方向へ進退移動自在となるよう配設され、移動レンズ66を保持する移動枠65と、固定枠55,57内で固定され、移動枠65を進退自在に収容して、移動枠65との当接によって撮影光軸Oの一方向への移動を規制するストッパ60を備え、観察光学系33の一方の焦点距離を実現するように微調整自在な補正枠47と、を具備する。
