PURPOSE: To transmit an image of high quality faithful to an original picture by reading out the original picture, extracting connection points to be points having large curvatures in the sequence of contour points and approximating between adjacent connection points by a straight line, a circle, a circular arc, a free curve, or the like.

CONSTITUTION: A picture is read out and divided into blocks with reference size by a picture dividing device Δ. Each divided picture is converted into a binary image consisting of white and black picture elements and an outline (the sequence of contour points) to be a boundary between a white area and a black area is extracted by a contour point sequence extracting device B. A connection point extracting device approximates a group of contour point sequences by a sectional polynomial and finds out its curvature. A complete roundness is separated and points having large curvatures out of the remaining contour point sequence are set up as connection points. A compressed data generating device approximates between connecting points by a straight line, a circular arc, a free curve, or the like. The obtained connection points and the parameter or the straight line, the circular arc or the free curve are stored in a compressed data storing device P as data expressing the divided picture. These data are transmitted through a telephone line or the like as communication data.