A sound signal decoding device comprising: a first decoding unit that is adapted to obtain first decoded values by decoding a first code, the first decoded values corresponding to line spectrum pair parameters of more than one order; an index calculation unit adapted to calculate an index Q and/or an index Q', with p being a prediction order and T being a predetermined order satisfying T ≤ p, the index Q being obtained using quantized line spectrum pair parameters ^θ f , ^θ f , ..., ^θ f [p] corresponding to the first code by θ ̅ = 1 T − 1 ∑ i T − 1 θ ^ f i + 1 − θ ^ f i Q = 1 T − 1 ∑ i T − 1 θ ̅ − θ ^ f i + 1 + θ ^ f i 2 and the index Q' being obtained using quantized line spectrum pair parameters ^θ f , ^θ f , ..., ^θ f [p] corresponding to the first code by Q ′ = min i ∈ 1 , ... , T − 1 θ ^ f i + 1 − θ ^ f i or Q ′ = min i ∈ 1 , ... , T − 1 min θ ^ f i + 1 − θ ^ f i , θ ^ f 1 ] ; a second decoding unit that is adapted to obtain second decoded values of more than one order by decoding a second code only if the index Q is larger than or equal to a predetermined threshold value Th1 and/or the index Q' is smaller than or equal to a predetermined threshold value Th1'; and an addition unit that is adapted to obtain third decoded values corresponding to the line spectrum pair parameters of more than one order by adding the first decoded values and the second decoded values of corresponding orders only if the index Q is larger than or equal to the predetermined threshold value Th1 and/or the index Q' is smaller than or equal to the predetermined threshold value Th1', wherein orders of the second decoded values are lower than orders of the first decoded values, and as for orders higher than the orders of the second decoded values, the addition unit uses the first decoded values of corresponding orders as the third decoded values without change. a first decoding unit that is adapted to obtain first decoded values by decoding a first code, the first decoded values corresponding to line spectrum pair parameters of more than one order; an index calculation unit adapted to calculate an index Q and/or an index Q', with p being a prediction order and T being a predetermined order satisfying T ≤ p, the index Q being obtained using quantized line spectrum pair parameters ^θ f , ^θ f , ..., ^θ f [p] corresponding to the first code by θ ̅ = 1 T − 1 ∑ i T − 1 θ ^ f i + 1 − θ ^ f i Q = 1 T − 1 ∑ i T − 1 θ ̅ − θ ^ f i + 1 + θ ^ f i 2 and the index Q' being obtained using quantized line spectrum pair parameters ^θ f , ^θ f , ..., ^θ f [p] corresponding to the first code by Q ′ = min i ∈ 1 , ... , T − 1 θ ^ f i + 1 − θ ^ f i or Q ′ = min i ∈ 1 , ... , T − 1 min θ ^ f i + 1 − θ ^ f i , θ ^ f 1 ] ; a second decoding unit that is adapted to obtain second decoded values of more than one order by decoding a second code only if the index Q is larger than or equal to a predetermined threshold value Th1 and/or the index Q' is smaller than or equal to a predetermined threshold value Th1'; and an addition unit that is adapted to obtain third decoded values corresponding to the line spectrum pair parameters of more than one order by adding the first decoded values and the second decoded values of corresponding orders only if the index Q is larger than or equal to the predetermined threshold value Th1 and/or the index Q' is smaller than or equal to the predetermined threshold value Th1', wherein orders of the second decoded values are lower than orders of the first decoded values, and as for orders higher than the orders of the second decoded values, the addition unit uses the first decoded values of corresponding orders as the third decoded values without change. <EOS>