PURPOSE: To hold a background component at an invariably-constant level by correcting by detecting a waveform following up the background component from a picture signal itself, and by dividing the original picture signal on the basis of the waveform.
CONSTITUTION: Camera 21, bonded to the eyepiece of microscope 22, takes a picture of a microscope image. A video signal obtained by photoelectrically converting the microscope image by camera 21 controlled by camera control part 23 is supplied to black-level clamping circuit 24 to set the black level of the signal to zero forcibly. Then, output picture signal (a) is supplied to peak holding circuit 25 and also to one input A of arithmetic circuit 26. Signal C prescribed in the scan period of the output of control part 23, on the other hand, is supplied to circuit 24 and also to 1st switching circuit 27 and MMV28, and one terminal of circuit 27 is connected to resistor 29. Further, circuit 25 is connected to connection point Q and output (b) is inputted to input B of arithmetic circuit 26, where A is divided by B; after the result is multiplied by constant voltage VR and outputted, the product is supplied to picture processor 33.