A signal processing device (100, 200) that outputs received data upon receipt of a modulated signal that is orthogonal frequency division modulated by a plurality of subcarriers, the signal processing device comprising: an input section that extracts a predetermined number of input data from the modulated signal that is in a time series; a window function processing section that is capable of exercising control to determine whether or not to perform a window function process on the predetermined number of input data; an FFT processing section that performs an FFT process on data output from the window function processing section; and a narrow-band noise detection/determination section; wherein the narrow-band noise detection/determination section detects the degree of coincidence between the frequency of narrow-band noise included in the modulated signal and the frequencies of the subcarriers, and exercises control to determine in accordance with the detected degree of coincidence whether the window function processing section should perform the window function process on the input data and supply the resulting processed data to the FFT processing section or supply the input data to the FFT processing section without performing the window function process on the input data, characterized in that: the FFT processing section acts as a first FFT processing section, wherein the narrow-band noise detection/determination section includes a second FFT processing section that performs an FFT process on the input data to calculate electrical power at the frequency of each of the subcarriers, wherein, if a predetermined threshold value is exceeded by the electrical power at two neighboring subcarrier frequencies, the narrow-band noise detection/determination section allows the window function processing section to perform the window function process, and wherein, if the threshold value is exceeded by the electrical power at only one subcarrier frequency, the narrow-band noise detection/determination section inhibits the window function processing section from performing the window function process. an input section that extracts a predetermined number of input data from the modulated signal that is in a time series; a window function processing section that is capable of exercising control to determine whether or not to perform a window function process on the predetermined number of input data; an FFT processing section that performs an FFT process on data output from the window function processing section; and a narrow-band noise detection/determination section; wherein the narrow-band noise detection/determination section detects the degree of coincidence between the frequency of narrow-band noise included in the modulated signal and the frequencies of the subcarriers, and exercises control to determine in accordance with the detected degree of coincidence whether the window function processing section should perform the window function process on the input data and supply the resulting processed data to the FFT processing section or supply the input data to the FFT processing section without performing the window function process on the input data, characterized in that: the FFT processing section acts as a first FFT processing section, wherein the narrow-band noise detection/determination section includes a second FFT processing section that performs an FFT process on the input data to calculate electrical power at the frequency of each of the subcarriers, wherein, if a predetermined threshold value is exceeded by the electrical power at two neighboring subcarrier frequencies, the narrow-band noise detection/determination section allows the window function processing section to perform the window function process, and wherein, if the threshold value is exceeded by the electrical power at only one subcarrier frequency, the narrow-band noise detection/determination section inhibits the window function processing section from performing the window function process. the FFT processing section acts as a first FFT processing section, wherein the narrow-band noise detection/determination section includes a second FFT processing section that performs an FFT process on the input data to calculate electrical power at the frequency of each of the subcarriers, wherein, if a predetermined threshold value is exceeded by the electrical power at two neighboring subcarrier frequencies, the narrow-band noise detection/determination section allows the window function processing section to perform the window function process, and wherein, if the threshold value is exceeded by the electrical power at only one subcarrier frequency, the narrow-band noise detection/determination section inhibits the window function processing section from performing the window function process.