The airtightness between the holding cylinder and the cover glass can be improved without maintaining the accuracy of the cover glass attachment and without the joining member flowing into the tip surface of the optical lens, and a wide-angle field of view can be secured with a small diameter. An optical unit and an endoscope are provided. A spacer 144 is disposed between the cover glass position restricting portion 136 of the holding cylinder 132 of the optical unit 10 and the cover glass 108. The position of the cover glass 108 in the optical axis direction is restricted by the cover glass position restricting portion 136 via the spacer 144. The outer diameter D1 of the first end surface 144A of the spacer 144 is smaller than the inner diameter D2 of the cover glass fixing portion 134 of the holding cylinder 132. A solder pool portion is provided in a region 156 surrounded by the side surface 144C of the spacer 144, the cover glass fixing portion 134, and the cover glass position restricting portion 136.カバーガラスの取り付け精度を維持しつつ、かつ光学レンズの先端面に接合部材が流れ込むことなく、保持筒とカバーガラスとの気密性を高めることができ、更に細径で広角視野を確保することができる光学ユニット及び内視鏡を提供する。光学ユニット１０の保持筒１３２のカバーガラス位置規制部１３６とカバーガラス１０８との間にスペーサ１４４が配置される。カバーガラス１０８は、スペーサ１４４を介してカバーガラス位置規制部１３６に光軸方向の位置が規制される。スペーサ１４４の第１端面１４４Ａの外径Ｄ１は、保持筒１３２のカバーガラス固定部１３４の内径Ｄ２よりも小さい。スペーサ１４４の側面１４４Ｃとカバーガラス固定部１３４とカバーガラス位置規制部１３６とによって囲まれる領域１５６に半田溜まり部が設けられる。
