PURPOSE: To obtain a good binary coded image having no blur, by measuring the signal level of a picture element over the entire image and deciding the slice level of the image.

CONSTITUTION: A multivalue image signal 14 delivered from a photoelectric converting device 11 is stored in an image storing device 15 and then fed to an intra-image peak value detecting circuit 16 to detect the intra-image peak value 17 representing the entire image. A reference slice level deciding circuit 18 decides the slice level to the entire image from the peak value 17. The signal 14 from the device 15 is fed to a quantizing circuit 20 to be binary coded. Thus a binary coded image signal is delivered. The circuit 18 gives an upper a limit to the slice level by the peak value 17 to prevent the occurrence of blur to the binary coded image which is caused by an excessively high slice level.