PURPOSE: To enable to the movement of clouds, the amount of clouds and the amount of sun shine, by providing the reflecting mirror introducing the image of the sum to the outside of the pick up image sensor on the light axis of the TV camera.

CONSTITUTION: The light 1 representing te condition 7 of sky including the sun 8 and clouds 9 is incident on the TV camera 5 via the lenses 2 and 4. The reflecting mirror 3 is located on the center of the focus surface of the lens 2 on the light axis of the TV camera, and the image of the sun formed is reflected to the upper outside direction with the mirror surface of almost the same size. Further, after the image of other sky is diverged through the focus plane of te lens 2, it is returned again into parallel lights with the lens 4 and is incident to the camera 5. Thus, the shadow of the reflection mirror and the support rod and the condition of sky are formed on the focus of the lens 2 on the screen of the camera 5, and the movement of clouds, the amount of clouds and the amount of sun shine can simply be observed.