A picture encoding method for generating a prediction signal using spatial inter-pixel prediction and encoding a picture using a prediction residual signal which is a difference between the prediction signal and an original signal that includes a block that is a processing unit of coding, transform, or prediction and that is a region in which coding is performed using intra-prediction, the picture encoding method comprising: a step of generating an intra-prediction signal corresponding to a designated intra-prediction mode using a reference pixel of the intra-prediction that is referred to when the intra-prediction is performed, the reference pixel being present in the vicinity of the block, the reference pixel being determined in accordance with a size of the block and the intra-prediction mode, the reference pixel being present in an intra-reference pixel region in which reference pixels of the intra-prediction necessary for all intra-prediction modes are present; a step of generating an intra-prediction residual signal representing a difference between the generated intra-prediction signal and the original signal; and a step of encoding the intra-prediction residual signal, the method being characterized by comprising: a step (S206, S216) of setting, for the reference pixel, a tap length of an interpolation filter necessary for generating a value for the reference pixel based on one or both of the size of the block in the original signal and a quantization parameter of the block; and a step (S207, S217) of performing a filtering process which generates the value for the reference pixel by an interpolation process using the interpolation filter corresponding to the set tap length based on the intra-prediction mode and decoded pixels that are present in the intra-reference pixel region for the block and that are determined in accordance with the intra-prediction mode used for generating the value for the reference pixel, wherein, in the step of setting the tap length of the interpolation filter, if the size of the block is less than or equal to a threshold value, the tap length is set to be longer than when the size of the block is greater than the threshold value and/or if a quantization step size represented by the quantization parameter of the block is less than or equal to a threshold value, the tap length is set to be longer than when the quantization step size is greater than the threshold value. a step of generating an intra-prediction signal corresponding to a designated intra-prediction mode using a reference pixel of the intra-prediction that is referred to when the intra-prediction is performed, the reference pixel being present in the vicinity of the block, the reference pixel being determined in accordance with a size of the block and the intra-prediction mode, the reference pixel being present in an intra-reference pixel region in which reference pixels of the intra-prediction necessary for all intra-prediction modes are present; a step of generating an intra-prediction residual signal representing a difference between the generated intra-prediction signal and the original signal; and a step of encoding the intra-prediction residual signal, the method being characterized by comprising: a step (S206, S216) of setting, for the reference pixel, a tap length of an interpolation filter necessary for generating a value for the reference pixel based on one or both of the size of the block in the original signal and a quantization parameter of the block; and a step (S207, S217) of performing a filtering process which generates the value for the reference pixel by an interpolation process using the interpolation filter corresponding to the set tap length based on the intra-prediction mode and decoded pixels that are present in the intra-reference pixel region for the block and that are determined in accordance with the intra-prediction mode used for generating the value for the reference pixel, a step (S206, S216) of setting, for the reference pixel, a tap length of an interpolation filter necessary for generating a value for the reference pixel based on one or both of the size of the block in the original signal and a quantization parameter of the block; and a step (S207, S217) of performing a filtering process which generates the value for the reference pixel by an interpolation process using the interpolation filter corresponding to the set tap length based on the intra-prediction mode and decoded pixels that are present in the intra-reference pixel region for the block and that are determined in accordance with the intra-prediction mode used for generating the value for the reference pixel, wherein, in the step of setting the tap length of the interpolation filter, if the size of the block is less than or equal to a threshold value, the tap length is set to be longer than when the size of the block is greater than the threshold value and/or if a quantization step size represented by the quantization parameter of the block is less than or equal to a threshold value, the tap length is set to be longer than when the quantization step size is greater than the threshold value.