An encoding device 1 includes: a transformer 13 configured to calculate an orthogonal transform coefficient by performing an orthogonal transformation process on a residual image indicating a difference between the input image and a predicted image of the input image; a quantizer 14 configured to generate quantization coefficient by quantizing the orthogonal transform coefficient based on a quantization parameter; an entropy encoder 24 configured to generate encoded data by encoding the quantization coefficient; an image decoder 10 configured to restore an orthogonal transform coefficient from the quantization coefficient based on the quantization parameter and generate a pre-filtering image by adding the predicted image to a residual image restored by performing inverse orthogonal transformation on the orthogonal transform coefficient; and a deblocking filter 18 configured to perform a filtering process on the pre-filtering image and control a filtering strength depending on a result of comparison between a luminance signal level of the pre-filtering image and a luminance threshold value.