To reduce the increase in operation quantity regarding address generation when a fixed code book search process of an ACELP(algebraic code excitation linear prediction) voice encoding system is actualized by a signal processing LSI such as a DSP.

This device is equipped with a threshold calculating means 101 which calculates a threshold for controlling the frequency of search of an algebraic code book in the fixed code book search process, a narrowing-down search approach means 102, which narrows down a search place of the algebraic code book according to the threshold, and a pulse position search means 103 which searches an algebraic code book on the basis of the result of the narrowing-down search approach means 102.