A signal processing apparatus comprising: a signal compression unit configured to compress a reception signal so as to have a predetermined signal level or lower; and a decoding unit configured to decode transmission data transmitted from a transmitter side, the transmission data being included in the reception signal compressed by the signal compression unit so as to have the signal level or lower, wherein the signal compression unit includes an approximate replica generation unit configured to generate an approximate replica signal reproducing large amplitude changes of the reception signal, the approximate replica generation unit including a phase detection unit configured to detect a phase of the reception signal, an envelope detection unit configured to detect an envelope of the reception signal, a complex composition unit configured to subject a phase detection result of the reception signal obtained by the phase detection unit and an envelope detection result of the reception signal obtained by the envelope detection unit to complex composition, and a determination unit configured to determine whether or not the envelope detection result of the reception signal obtained by the envelope detection unit exceeds the signal level, and wherein the signal compression unit further includes a subtraction unit configured to subtract the approximate replica signal generated by the approximate replica generation unit from the reception signal, wherein the subtraction unit is configured to subtract, as the approximate replica signal, a complex composition result of the phase detection result and the envelope detection result obtained by the complex composition unit from the reception signal, with respect to a portion of the reception signal with respect to which the determination unit has determined that the envelope detection result exceeds the signal level. a signal compression unit configured to compress a reception signal so as to have a predetermined signal level or lower; and a decoding unit configured to decode transmission data transmitted from a transmitter side, the transmission data being included in the reception signal compressed by the signal compression unit so as to have the signal level or lower, wherein the signal compression unit includes an approximate replica generation unit configured to generate an approximate replica signal reproducing large amplitude changes of the reception signal, the approximate replica generation unit including a phase detection unit configured to detect a phase of the reception signal, an envelope detection unit configured to detect an envelope of the reception signal, a complex composition unit configured to subject a phase detection result of the reception signal obtained by the phase detection unit and an envelope detection result of the reception signal obtained by the envelope detection unit to complex composition, and a determination unit configured to determine whether or not the envelope detection result of the reception signal obtained by the envelope detection unit exceeds the signal level, and a phase detection unit configured to detect a phase of the reception signal, an envelope detection unit configured to detect an envelope of the reception signal, a complex composition unit configured to subject a phase detection result of the reception signal obtained by the phase detection unit and an envelope detection result of the reception signal obtained by the envelope detection unit to complex composition, and a determination unit configured to determine whether or not the envelope detection result of the reception signal obtained by the envelope detection unit exceeds the signal level, and wherein the signal compression unit further includes a subtraction unit configured to subtract the approximate replica signal generated by the approximate replica generation unit from the reception signal, wherein the subtraction unit is configured to subtract, as the approximate replica signal, a complex composition result of the phase detection result and the envelope detection result obtained by the complex composition unit from the reception signal, with respect to a portion of the reception signal with respect to which the determination unit has determined that the envelope detection result exceeds the signal level.