Picture having a band of 6 MHz is distributed to the set-top box (STB) 14 via the compression encoder 11, the distribution server 12, and the network 13. The low-pass filter 151 in the picture quality monitoring apparatus 15 removes high-frequency components of an inputted digital signal and inputs luminance signal, the band of which is limited to 4 MHz, into the PSNR calculator 153. The Y/C separator 152 separates a luminance signal from NTSC analog composite signal, which are sent out from the set-top box 14. The separated luminance signal has a band of 4 MHz. The PSNR calculator 153 calculates PSNR between the luminance signal from the low-pass filter 151 and the luminance signal from the Y/C separator 152.