PURPOSE: To attain an inexpensive coder by saturating a coder output to an overload code to a residual difference signal between a real value being larger than a set overload level and an estimated value thereby reducing the dynamic range for the share.

CONSTITUTION: An echo cancellor 3 is provided among a reception section 1 and a transmission section 2 at the opposite party and an echo device 4 made of a 4/2-wire converting section viewed from terminals 10, 11. The cancellor 3 consists of a coder coding a transmission signal xj, an operating circuit 6, a decoder 7 decoding an estimated echo line response yj', an analog subtraction circuit 8 subtracting an estimated value yj' from an actual echo response yj, and a coder 9 coding a residual difference signal ej. The overload level of the coder 9 is set lower than the maximum level of the signal ej so as to saturate the output of the coder to the overload code to the residual difference signal ej larger than the set level. Thus, the number of bits of the coder is reduced and the coder is constituted with a low cost.