PURPOSE: To shorten transmission time as much as possible by dividing one scanning line into sections, and by transmitting a variation state signal for gradations of a picture in each section and an information signal for the picture.

CONSTITUTION: A picture is scanned by, for example, a high-speed scanning part 1 and an obtained information singal is stored in a buffer memory 2 and also differentiated by a differentiating circuit 3 to detect the variation state of the picture. Then, an absolute-value amplifier 4 finds the rate of the variation and on the basis of the hold value of a maximum value in each section, a read speed control circuit 6 determines the transmission speed of each section. Then, the picture information signal stored in the buffer memory 2 is read out at a low speed when the maximum variation rate of the section is high or at a high speed when low, and then sending to a transmission line through a switcher 9 and a modulator 10.