A Tu delay section (110) delays an analog-to-digital converted OFDM signal S01 by a time corresponding to an effective symbol period Tu. A correlation signal of an output of the Tu delay section (110) and OFDM signal S01 is obtained using a correlation calculating section (120). A delay section (130) outputs at least one delayed correlation signal obtained by delaying a correlation signal S02. Next, an adding section (140) performs addition of the correlation signal S02 and the delayed correlation signal, and then an interval integration section (150) performs transfer integration over a definite interval on a result of the addition. Then, a symbol period smoothing section (160) smoothes a result of the transfer integration for an interval of the effective symbol period of the OFDM signal S01, and then a window position detection section (170) calculates window position information from an output of the symbol period smoothing section (160).