PURPOSE: To reduce the cost of a titled coding device as a whole, by providing two D/A converters within a local decoder and applying the added signal of the outputs of these converters to the reference signal.

CONSTITUTION: The PAM input signal given from a terminal IN is fed to a comparator 11 in response to the polarity of the PAM input signal and along with the reference signal E that passed through operational amplifiers 13 and 14 either one of which is turned on by a control switch 15. The decided bits are fed successively to a terminal OUT and then delivered in the form of the converted 8-bit output signal. These decided bits are successively stored in an approximate register 16, and the register 16 delivers a nonlinear code corresponding to the analog level of the bit which is lower by a digit than the decided bit. A local signal generator 400 applies the code supplied from the register 16 to the 8-bit linear D/A converters 17 and 18 via a converter 19 and in the form of an 8-bit nonlinear code of two groups. The added signal of outputs of the converters 17 and 18 is delivered as a reference signal E to be used by the comparator 11 to decide the next bit.