According to the present invention, a shift amount Sj−1 of the previous frame is held in a shift amount buffer of an integer signal coder. At least as many last sample values in the previous frame as the number of an order P used in linear predictive analysis are held in a sample buffer of the integer signal coder. The last P sample values in the previous frame held in the sample buffer of the integer signal coder are corrected in an interframe correction section by Sj-Sj−1 on the basis of the shift amount Sj of the current frame and the shift amount Sj−1 of the previous frame determined by a shift amount determining section.