A speech analysis unit and a window locating unit are implemented in a speech encoding apparatus. The speech encoding apparatus encodes input speech per analysis frame defined having a fixed length and is offset at fixed interval. the speech analysis unit extracts frequency spectrum parameters of the input speech taken within an analysis window. The location of the analysis window is specified by the window locating unit. The window locating unit selects the location of the analysis window which is used in extracting the frequency spectrum characteristic parameters at the speech analysis unit. In this case, depending upon the characteristic parameter of the input speech within and near the frame concerned, the window locating unit selects the location of the analysis window within the range which is not to be exceeding the range of the frame concerned.