An encoding method comprising: an encoding mode selecting step of selecting a second encoding mode when an evaluation value is a second reference value or less, selecting a first encoding mode other than the second encoding mode when the second encoding mode is not selected, and generating mode information representing a selected encoding mode, wherein the evaluation value corresponds to the number of samples which correspond to values less than a first reference value among a predetermined number of input samples, and the second encoding mode is a mode in which a normalization value that is a representative value of the predetermined number of samples is quantized to obtain a quantized normalization value and a normalization-value quantization index corresponding to the quantized normalization value, a difference value for each sample that is obtained by subtracting a value corresponding to the quantized normalization value from a value corresponding to the magnitude of a sample is set as a quantization candidate corresponding to the sample when the difference value is positive and the sample is positive, the sign of the difference value is reversed and the result is set to the quantization candidate corresponding to the sample when the difference value is positive and the sample is negative, and a plurality of quantization candidates are jointly vector-quantized to obtain a vector quantization index; and an encoding step of encoding the predetermined number of samples by the first encoding mode or the second encoding mode that is selected in the encoding mode selecting step, characterized in that: the first encoding mode is a mode in which the vector quantization index is obtained by vector-quantizing according to a vector quantization mode in which non-zero quantized values are obtained only for some of the predetermined number of samples and zero quantized values are obtained for the remaining samples; and the second encoding mode includes a process of setting zero as the quantization candidate corresponding to each of the samples when the difference value is not positive. an encoding mode selecting step of selecting a second encoding mode when an evaluation value is a second reference value or less, selecting a first encoding mode other than the second encoding mode when the second encoding mode is not selected, and generating mode information representing a selected encoding mode, wherein the evaluation value corresponds to the number of samples which correspond to values less than a first reference value among a predetermined number of input samples, and the second encoding mode is a mode in which a normalization value that is a representative value of the predetermined number of samples is quantized to obtain a quantized normalization value and a normalization-value quantization index corresponding to the quantized normalization value, a difference value for each sample that is obtained by subtracting a value corresponding to the quantized normalization value from a value corresponding to the magnitude of a sample is set as a quantization candidate corresponding to the sample when the difference value is positive and the sample is positive, the sign of the difference value is reversed and the result is set to the quantization candidate corresponding to the sample when the difference value is positive and the sample is negative, and a plurality of quantization candidates are jointly vector-quantized to obtain a vector quantization index; and an encoding step of encoding the predetermined number of samples by the first encoding mode or the second encoding mode that is selected in the encoding mode selecting step, characterized in that: the first encoding mode is a mode in which the vector quantization index is obtained by vector-quantizing according to a vector quantization mode in which non-zero quantized values are obtained only for some of the predetermined number of samples and zero quantized values are obtained for the remaining samples; and the second encoding mode includes a process of setting zero as the quantization candidate corresponding to each of the samples when the difference value is not positive. the first encoding mode is a mode in which the vector quantization index is obtained by vector-quantizing according to a vector quantization mode in which non-zero quantized values are obtained only for some of the predetermined number of samples and zero quantized values are obtained for the remaining samples; and the second encoding mode includes a process of setting zero as the quantization candidate corresponding to each of the samples when the difference value is not positive.