In order to enhance the speed of a processing necessary for setting the factor of a filter and further maintain the accuracy of the filter, a digital processing apparatus includes: a Fourier transform unit that Fourier transforms a time domain digital signal, thereby generating N frequency domain signals; a filter unit that uses N first factors to process the frequency domain signals in the frequency domain; an inverse Fourier transform unit that transforms the frequency domain signals as processed by the filer unit to a time domain digital signal; a low accuracy factor calculation unit that uses m second factors to calculate N first A factors; a high accuracy factor calculation unit that includes a factor division unit for calculating respective ratios of N third factors to the N first A factors and that also includes a factor variable unit for calculating N first B factors varying stepwise from one to the respective ratios; a multiplication unit that multiplies the first A factors by the first B factors, thereby calculating the N first factors; and a control unit that controls the low accuracy factor calculation unit and high accuracy factor calculation unit by causing only the low accuracy factor calculation unit to operate with the first B factors being set to one and thereafter causing the high accuracy factor calculation unit to calculate the first B factors based on the third factors.