An FFT operational device includes memory banks, an FFT operational circuit, and an FFT memory control circuit. The memory banks can overwrite pieces of data to specified address locations simultaneously or read out the data from the locations simultaneously. The operational circuit receives operands read out from the banks simultaneously to perform an FFT operation processing on the operands to output operation results simultaneously, and repeats the FFT operation processing a predetermined number of times. The memory control circuit receives the operation results output from the operational circuit simultaneously, and changes the order of the data in such a way that the pieces of data required for the operational circuit in the successive operation processing will be provided simultaneously. The resultant data are overwritten to the memory banks. The operational device thereby performs FFT or IFFT processing on hardware, the storage capacity thus being reduced with operational speed increased.