According to one embodiment, a scaling decision device includes a first decision unit and a second decision unit. The first decision unit decides, based on a plurality of input signals, a K-th smallest signal of the plurality of input signals or a range to which the K-th smallest signal belongs of a plurality of ranges which classify the plurality of input signals by intensities. The second decision unit decides, based on a decision result of the first decision unit, a scaling value which prevents the K-th smallest signal from being submerged in quantization errors by normalization.