PURPOSE: To instantaneously reproduce the synchronizing frequency of the transmission side on the reception side almost without changing the degree of redundancy even when the amount of image data generated at respective frames is considerably changed.

CONSTITUTION: Inputted image information S1 is quantized by a quantization circuit 2, encoded data S4 are generated by performing variable length encoding to quantized image data S2 at a variable length encoding circuit 3, and these generated data are supplied to a redundant code adding circuit 5. At this redundant code adding circuit 5, redundant code added data S5 are generated by adding a transmission synchronizing signal or an error correct code to the encoded data S4 for each small transmission block and sent to an image synchronizing signal adding circuit 7, and an image synchronizing signal is added. Thus, the synchronizing signal of an image signal can be reproduced on the reception side, and an image frame signal synchronizing the phase with the transmission side can be speedily and surely reproduced.