Speech signal transmission apparatus and method that multiplex and packetize coded information

A speech signal transmission apparatus multiplexes, packetizes, and sends first coded information coded in a normal state and second coded information used for improving the quality of decoded speech when a frame loss occurs. A first error calculating section calculates a first error signal between a target signal and a synthesized signal generated by an adaptive codebook, and a second error calculating section calculates a second error signal between the target signal and a synthesized signal generated by a fixed codebook. An error signal ratio calculating section calculates the ratio of the first error signal to the second error signal. A speech frame classifying section classifies a speech frame according to the magnitude of the ratio, and a decision section decides whether or not to multiplex the second coded information based on the classification result.