To provide an adjacent-channel leaking power computing device which can precisely compute adjacent-channel leaking power based upon the base-band signal outputted by a base-band device 20.

The adjacent-channel leaking power computing device which computes the adjacent-channel leaking power based upon the base-band signal is equipped with an A/D conversion part which converts the base-band signal as an analog signal into a digital signal, a complex Fourier transformation part which performs complex Fourier transformation of the base-band signal converted by the A/D conversion part, and a computation part which computes the adjacent-channel leaking power based upon the base-band signal according to the processing result of the complex Fourier transformation.