A determination apparatus for determining communication availability in an Orthogonal Frequency Division Multiplexing, OFDM, scheme communication system, the determination apparatus comprising: a reception unit configured to receive a wireless signal including OFDM symbols in which a pilot signal is inserted at a constant insertion frequency in a frequency axis direction, an obtaining unit configured to obtain a discrete sample signal by sampling the wireless signal, a correlation value calculation unit configured to calculate autocorrelation values of the discrete sample signal for time shift amounts that are defined in advance according to the constant insertion frequency, based on characteristics of Inverse Fast Fourier Transform and autocorrelation in which 1) each of the OFDM symbols is based on a symbol of as many as N time-domain samples formed by applying Inverse Fast Fourier Transform to as many as N data items and, in a case where one third of the N data items include non-zero data, content of the symbol is equal to repetitions of one third portion of N time-domain samples, and in a case where one sixth of the N data items include non-zero data, content of the symbol is equal to repetitions of one sixth portion of N time- domain samples; and 2) in the case where the content of the symbol is equal to repetitions of one third portion of N time-domain samples, autocorrelation value for that OFDM symbol has its peak, not only in the case where the time shift amount is equal to zero and equal to N, but also in the case where the time shift amount is equal to N/3 and 2N/3, and a determination unit configured to determine the communication availability in the communication system based on at least a result of determination whether the autocorrelation values for the time shift amounts have a peak or not, wherein, in a case where a first autocorrelation value of the discrete sample signal for a first time shift amount equal to N/3 has a first peak and a second autocorrelation value of the discrete sample signal for a second time shift amount equal to 2N/3 has a second peak, the determination unit is further configured to determine the communication availability in the communication system by estimating a degree of congestion of the communication system from a ratio between the first peak and the second peak a reception unit configured to receive a wireless signal including OFDM symbols in which a pilot signal is inserted at a constant insertion frequency in a frequency axis direction, an obtaining unit configured to obtain a discrete sample signal by sampling the wireless signal, a correlation value calculation unit configured to calculate autocorrelation values of the discrete sample signal for time shift amounts that are defined in advance according to the constant insertion frequency, based on characteristics of Inverse Fast Fourier Transform and autocorrelation in which 1) each of the OFDM symbols is based on a symbol of as many as N time-domain samples formed by applying Inverse Fast Fourier Transform to as many as N data items and, in a case where one third of the N data items include non-zero data, content of the symbol is equal to repetitions of one third portion of N time-domain samples, and in a case where one sixth of the N data items include non-zero data, content of the symbol is equal to repetitions of one sixth portion of N time- domain samples; and 2) in the case where the content of the symbol is equal to repetitions of one third portion of N time-domain samples, autocorrelation value for that OFDM symbol has its peak, not only in the case where the time shift amount is equal to zero and equal to N, but also in the case where the time shift amount is equal to N/3 and 2N/3, and a determination unit configured to determine the communication availability in the communication system based on at least a result of determination whether the autocorrelation values for the time shift amounts have a peak or not, wherein, in a case where a first autocorrelation value of the discrete sample signal for a first time shift amount equal to N/3 has a first peak and a second autocorrelation value of the discrete sample signal for a second time shift amount equal to 2N/3 has a second peak, the determination unit is further configured to determine the communication availability in the communication system by estimating a degree of congestion of the communication system from a ratio between the first peak and the second peak