To improve the utilization efficiency of light by concentratedly irradiating an observation part with light and also to make it possible to easily wipe off dirt even if the tip of a borescope is smeared with oil, etc.

In the peripheral part of an image incoming end part 6in of an image guide 6 inserted in a tube 2, an illumination light optical fiber light guide 7 is coaxially arranged, and its light emitting end part 7out is placed closer to the objective lens 3 than to the focus position of the objective lens 3. Thus, the emitted light diverged from the light emitting end part 7out travels along an optical axis straight going to the objective lens 3, and then travels along a refracted optical axis in the direction of passing through the focus at the observation piece side of the objective lens, and most of the light can be projected within a range observable by an image guide 6, and the utilization efficiency of light is improved. Moreover, since the tip opening part of the tube 2 into which the image guide 6 and light guide 7 are inserted is blocked by the objective lens 3, it is possible to wipe off dirt even if the tip is smeared with oil, etc.