1. Speech encoding method in a transmitter by using an additional bit allocation, comprising: dividing the speech signal into spectrum information and an excited signal component and generating standard coded bit streams by performing modeling, quantizing, and coding with respect to the spectrum information and the excited signal; obtaining errors between the quantized signal and the unquantized signal with respect to the excited signal component, and generating a coded bit streams by performing additional quantization with respect to the obtained errors; and multiplexing the bit streams obtained at each of the coders and transmitting the multiplexed bit streams to a receiver.