PURPOSE: To prevent a filter etc. from being left uncleaned, by projecting light from the one hand face of a light transmitting body and also photodetecting said projected light by the other face of the light transmitting body.

CONSTITUTION: A filter 1 which is a light transmitting body is supported by attaching threadably a frame 3 to the tip end of a lens guard 2 arranged to the circumference of a lens cylinder of a television camera. A projector 4 (e.g. a light emission diode) and a photodetector 5 (e.g. a phototransistor) are used for detecting optically a stain of the filter 1 and these are fixed to the inner circumferential surface of the frame of the filter 1 so that its optical axis crosses with the surface of the filter 1 each other and does not enter a field of vision of the television camera.