PROBLEM TO BE SOLVED: To provide an objective optical unit which prevents intense light such as laser beams from proceeding to a light receiving surface of an image pickup device after passing through the inside of a frame member where an optical filter is provided.SOLUTION: An objective optical unit 1 is coaxially equipped with a first holding hole 11 having a frame distal end opening 14 and a second holding hole 12 having a frame proximal end opening 15, and includes: a frame member 10 having a step surface opening 17 on a step surface 16 of the first holding hole 11 and the second holding hole 12 a first lens 31 which is arranged inside the first holding hole 11 and allows light from the outside to enter a second lens 32 which is arranged inside the second holding hole 12 and emits the light passing through the first lens 31 to the outside and a filter 40 for a laser beam which is arranged between the first lens 31 and the second lens 32 in the second holding hole 12. On an outer peripheral surface of the filter 40 for a laser beam, a male type screw-shaped part 41 is provided, and at least on an inner peripheral surface of the second holding hole 12 between the first lens 31 and the second lens 32, a female type screw-shaped part 18 to which the male type screw-shaped part 41 is screwed is provided.SELECTED DRAWING: Figure 2COPYRIGHT: (C)2017,JPO&INPIT【課題】レーザ光等の強い光が光学フィルタを設けた枠部材内を通過して撮像素子の受光面に向かうことを防止する対物光学ユニットを提供する。【解決手段】対物光学ユニット1は、同軸上に、枠先端開口14を有する第1保持孔11及び枠基端開口15を有する第2保持孔12が設けられ、第1保持孔11と第2孔12との段差面16に段差面開口17を有する枠部材10と、第1保持孔11内に配置され、外部からの光が入射する第1レンズ31と、第2保持孔12内に配置され、第1レンズ31を通過した光を外部に向けて出射する第2レンズ32と、第2保持孔12内であって第1レンズ31と第2レンズ32との間に配置されるレーザ光用フィルタ40と、を備え、レーザ光用フィルタ40の外周面には雄型ねじ状部41を設け、少なくとも第1レンズ31と第2レンズ32との間の第2保持孔12の内周面には雄型ねじ状部41が螺合する雌型ねじ状部18を設けた。【選択図】図2
