A compatible television signal encoder for encoding a television signal having a first signal and a second signal. The decoder includes a divider for dividing the wide aspect television signal into a main signal having the first signal and low-frequency components of the second signal multiplexed in the horizontal overscan regions of the first signal and an auxilary signal, an interpolator for producing an interpolating scanning field signal using a first scanning field signal of the main signal output from the divider, a field switch for replacing a second scanning field signal of the main signal with the interpolating scanning field signal output from the interpolator and an adder for adding the auxiliary signal from the divider to the signal output from the field switch.