1. A signal-processing apparatus comprising: candidate-detecting means for receiving an input signal including at least the first signal part and remaining signal parts in time-divided fashion, and for detecting, from the input signal, a candidate part of the first signal part in accordance with characteristic patterns of the input signal at prescribed time intervals; characteristic-extracting means for extracting characteristic data indicating the probability of the first signal part from the candidate part or from signal parts preceding and following the candidate part; and detecting means for detecting the first signal part in accordance with the characteristic data extracted by the characteristic-extracting means.