In a bandwidth compressed transmission system in which a frequency band of a television signal of 2:1 interlace system is compressed, on an encoder side, by interfield offset subsampling at a first sampling frequency corresponding to a substantially upper limit frequency of the television signal and, after an output signal thus subsampled is applied to a LPF for passing a signal component having an aliased portion resulting from the interfield offset subsampling and having a cut-off frequency substantially equal to one half of the first sampling frequency, by interframe offset subsampling at a second sampling frequency lower than the first sampling frequency and higher than one half of the first sampling, so that a multiplexed subsampled transmission signal which does not include an aliased portion of reverse phase results from the interframe offset subsampling. When decoding, interframe interpolation processing of a multiplexed subsampled transmission signal is performed to obtain a signal for a still picture portion, while intrafield interpolation processing of the same transmission signal is performed to obtain a signal for a motion picture portion. An interframe difference of the transmission signal is detected to obtain a motion detection signal. The signals for still and motion picture are linearly mixed in accordance with the motion detection signal. Motion can be detected completely by utilizing an interframe difference. An arrangement of a receiver can be made simple and improves picture quality.