PURPOSE: To reduce the amount of computations of preselection by a CELP coding method and to improve the quality of the coding.

CONSTITUTION: Estimated values of noise excitation vector energies after a synthesis are stored in a table 23 for every noise excitation vector or for every impulse response pattern of synthesis filters. Representative impulse response patterns of the filters are stored in a table 21. Impulse response series of the filters and the corresponding response patterns are selected by a selector 22 and energy estimated values are read from the table 23 employing these patterns and each noise excitation vector. The inner products of the waveforms after the synthesis and input voice waveforms are divided by the estimated values for every noise excitation vector and a set number of these candidate values are left intact starting with a larger value candidates.