There is provided a scalable encoding device capable of realizing a bandwidth scalable LSP encoding with high performance by improving the conversion performance from narrow band LSPs to wide band LSPs. The device includes: an autocorrelation coefficient conversion unit (301) for converting the narrow band LSPs of Mn order to an autocorrelation coefficients of Mn order; an inverse lag window unit (302) for applying a window which has an inverse characteristic of a lag window supposed to be applied to the autocorrelation coefficients; an extrapolation unit (303) for extending the order of the autocorrelation coefficients to (Mn+Mi) order by extrapolating the inverse lag windowed autocorrelation coefficients; an up-sample unit (304) for performing an up-sample process in the autocorrelation domain which is equivalent to an up-sample process in a time domain for the autocorrelation coefficients of the (Mn+Mi) order so as to obtain autocorrelation coefficients of Mw order; a lag window unit (305) for applying a lag window to the autocorrelation coefficients of Mw order; and an LSP conversion unit (306) for converting the lag windowed autocorrelation coefficients into LSPs.