PURPOSE: To reduce performance quantity by comprising a fixed code register of a hexagonal grating vector with one sample of +1 and the one of -1 and another vector with sample of 0.

CONSTITUTION: The fixed code register 2 is comprised of the hexagonal grating vector with one sample of +1 and the one of -1 and the another vector with sample of 0. In other words, an orthogonal transform part 60 generates an audible weight reproducing code vector AC' in which each code vector C of the hexagonal grating fixed code register 2 is intersected orthogonally to the optimum pitch prediction remainder vector AP in each pitch prediction remain der vector to which audible weight (A) is applied, however, at this time, a transform matrix H to intersect the vector C' orthogonally to the vector AP is shown as C'=HC, therefore, it can be found in an extremely simplified form AC'=AHC=HAn-HAm. In such a way, it is possible to remarkably reduce the number of times of multiplication.