An electronic device includes: a PHLCT circuit (15), which includes an input signal DCT coefficient computation module configured to compute DCT coefficients of an input signal of a subject block region in a plurality of block regions and block regions adjacent to the subject block region, respectively, an offset function DCT coefficient computation module configured to compute DCT coefficients of a gradient offset function, which offsets the gradient of the input signal at a block boundary between each subject block region and its adjacent block regions from the DCT coefficients of the input signal, and a residual computation module configured to compute a residual of the DCT coefficients of the input signal and the DCT coefficients of the gradient offset function; a quantization circuit configured to quantize the residual to obtain compressed data; and an entropy coding circuit (17) configured to encode the compressed data.