Disclosed is a decoding device (300a) that outputs an output signal by receiving, as an input, an encoded signal including a signal in which an original signal is encoded, the original signal being indicative of contents of at least one of image and audio, and the output signal being indicative of the contents, which decoding device includes a decoding process section (310) that generates a decoded signal be decoding the encoded signal, and a nonlinear process section (102) that generates a nonlinear process signal (i) in which positive and negative signs of a low-frequency-free signal are retained, which low-frequency-free signal is obtained by removing from the input signal at least a direct current of frequency components included in the decoded signal, and (ii) which broadly monotonically increases nonlinearly with respect to the low-frequency-free signal when values of the low-frequency-free signal are at least in the vicinity of 0; the nonlinear process signal is added to the decoded signal, to generate the output signal.