PURPOSE: To easily obtain a clear smaple picture on a picture screen by providing in a signal generation system a means that cuts off a signal, using a blanking signal in a scanning signal system and in a signal processing system a means that clamps the DC level of the signal, using this blanking signal.

CONSTITUTION: A shutter 6 is provided between a sample 4 and a detector 5 and the screening sections 6a and 6b of the shutter 6 are located so as to screen the light from the sample, synchronizing with a blanking signal. The outpt signal from the detector 5 is input as a picture signal to one input section of a pulse clamping circuit 11 through a preamplifier 10. The pulse clamping circuit 11 clamps such an input picture signal (a) and converts it into a picture signal (b). The picture signal (b) is clamped on to its DC level and a drift signal is remove from this picture signal (b). As a result, after the picture signal (b) from which the drift signal is removed is amplified by a picture amplifier 13, it is input to the brightness signal input terminal of a picture indicator 14.