Light irradiation apparatus and light irradiation system

This light irradiation device is provided with: an optical fiber; and a translucent optical path changing member that is disposed closer to the tip side than the optical fiber and that changes the optical path of the light incident from the optical fiber. The optical path changing member includes a base-end-side member disposed on the base-end side of the optical path changing member and a tip-end-side member disposed on the tip-end side of the optical path changing member. The base-end-side member and the tip-end-side member are in contact with each other to form a boundary surface, and the boundary surface is inclined with respect to a vertical plane of a central axis of the optical fiber. 光照射设备具备：光纤；以及透光性的光路变更部件，其配置于比光纤靠前端侧的位置，变更从光纤射入的光的光路。光路变更部件包括配置于光路变更部件的基端侧的基端侧部件和配置于光路变更部件的前端侧的前端侧部件。基端侧部件与前端侧部件相互接触而形成边界面，边界面相对于光纤的中心轴的垂直面倾斜。