A speech encoding method for encoding a speech according to code-excited linear prediction (CELP) comprising: analyzing the speech to obtain a linear prediction parameter; obtaining a linear prediction parameter code by encoding the linear prediction parameter; obtaining an adaptive code corresponding to a first time series vector from an adaptive codebook; obtaining, using a gain code, a first gain value corresponding to the first time series vector; evaluating a noise level of the speech using a code or coding result of at least one of the spectrum information, power information, and pitch information; obtaining a first weight and a second weight based on the evaluated noise level; obtaining an excitation code which corresponds to a second time series vector, the second time series vector being a weighted sum of a noise time series vector from a first excitation codebook weighted using the first weight and a non-noise time series vector from a second excitation codebook weighted using the second weight; obtaining, using the gain code, a second gain value corresponding to the second time series vector; obtaining the gain code corresponding to the first gain value and the second gain value, wherein each of the obtaining of the adaptive code, of the excitation code and of the gain code comprises calculating and minimizing a distance between a synthesized speech and the speech, wherein the synthesized speech is obtained by using the first and second time series vectors weighted with their respective gains and added; and outputting a speech code including the adaptive code, the linear prediction parameter code, the gain code, and the excitation code. analyzing the speech to obtain a linear prediction parameter; obtaining a linear prediction parameter code by encoding the linear prediction parameter; obtaining an adaptive code corresponding to a first time series vector from an adaptive codebook; obtaining, using a gain code, a first gain value corresponding to the first time series vector; evaluating a noise level of the speech using a code or coding result of at least one of the spectrum information, power information, and pitch information; obtaining a first weight and a second weight based on the evaluated noise level; obtaining an excitation code which corresponds to a second time series vector, the second time series vector being a weighted sum of a noise time series vector from a first excitation codebook weighted using the first weight and a non-noise time series vector from a second excitation codebook weighted using the second weight; obtaining, using the gain code, a second gain value corresponding to the second time series vector; obtaining the gain code corresponding to the first gain value and the second gain value, wherein each of the obtaining of the adaptive code, of the excitation code and of the gain code comprises calculating and minimizing a distance between a synthesized speech and the speech, wherein the synthesized speech is obtained by using the first and second time series vectors weighted with their respective gains and added; and outputting a speech code including the adaptive code, the linear prediction parameter code, the gain code, and the excitation code.