1. An apparatus for detecting speech segments of a speech signal, the apparatus comprising: an input unit adapted to receive the speech signal; a critical band dividing unit adapted to divide a critical band of the received speech signal into a plurality of regions according to noise frequency characteristics; a signal threshold calculation unit adapted to calculate a signal threshold for each of the plurality of regions; a noise threshold calculation unit adapted to calculate a noise threshold for each of the plurality of regions; a segment discriminating unit adapted to determine whether a current frame of the speech signal is a noise segment or a speech segment according to a log energy of each of the plurality of regions; and a signal processing unit adapted to control the input unit, critical band dividing unit, signal threshold calculation unit, noise threshold calculation unit and segment discriminating unit for detection of speech segments.