PURPOSE: To enable efficient compression of all observation images with an endoscope along with higher reproducibility of an original image by evaluating at least one of signals compressed by a plurality of compression means to produce an output to an image memory based on the evaluation.

CONSTITUTION: A selector 25 outputs data of R, G and B stored in respective memories 24 sequentially to a blocking circuit 26 and an image judging circuit 27 being controlled by a control signal generating section 31. The blocking circuit section processes the data sequentially and the image judging circuit performs an evaluation based on an original image from the selector and a compression image from the blocking circuit section to select a blocking circuit above a specified evaluation value. A selector 28 produces a signal inputted into any one of the blocking circuits to a forecast encoder 29 controlled by a picture quality judging circuit to generate a forecast error, which is outputted to an image memory 22. In this manner, compression is accomplished simultaneously with three kinds of blocking circuits and the images are judged. After a compression by a blocking, further compression is made by a forecast encoding, thereby achieving a higher compression efficiency.