PURPOSE: To obtain a binary-coded picture having a good picture quality from a picture whose surface density is high, etc., by taking OR of a frame picture binary-coded data of an original picture which has binary-coded multivalue data of the original picture by a high threshold level, and border picture data which has been binary-coded, referring to said frame picture data.

CONSTITUTION: Only 1 processing unit portion of a multivalue data (a) of an input picture is stored temporarily in a storage circuit 1, output data (b) from this circuit 1 is binary-coded by a threshold level in a high threshold binary-coding circuit 2, and its result is stored as frame picture data (g). Also, the output data (b) is differentiation-processed by a differentiation processing circuit 3, is binary-coded by a suitable threshold level, and a border line of the input picture is extracted, and is stored as border picture data (m). Subsequently, the frame picture data (g) from the binary-coding circuit 2, and the border picture data (m) from the processing circuit 3 are OR-processed by a logical processing circuit 4, binary-coded data (s) of the multivalue data (a) is outputted from the processing circuit 4, and a binary coded picture having a good picture quality is outputted from a picture whose surface is full of dirt, picture whose surface density is high, etc.