1. A noise detector for detecting noise contained in an input signal, the noise detector comprising: a noise discrimination portion having a plurality of discrimination portions to which the input signal is input, and a noise determination portion determining the noise based on individual discrimination results of the plurality of discrimination portions, wherein the noise discrimination portion comprises a frequency component discrimination portion discriminating the presence or absence of the noise based on a frequency component of the input signal, and at least one of a temporal change discrimination portion discriminating the presence or absence of the noise based on a temporal change of the input signal and a high-frequency component discrimination portion discriminating the presence or absence of the noise based on a high-frequency component of the input signal, the noise determination portion determines the noise based on a logical sum of individual discrimination results of the plurality of discrimination portions, the frequency component discrimination portion comprises a first filter portion and a second filter portion, the frequency component discrimination portion is configured to with the first and second filter portions, divide a whole power spectrum of the input signal into a first part power spectrum and a second part power spectrum, wherein the first part power spectrum is of a first frequency band containing frequencies at which characteristics of voice appear and the second part power spectrum is of a second frequency band containing frequencies at which characteristics of noise appear, and compare the first and second part power spectra to discriminate whether the input signal is a voice signal or a noise signal.