There is disclosed a motion detecting circuit used for a motion-adapted scanning line interpolating circuit in a television system. The motion detecting circuit comprises an inter-frame correlation detecting circuit for detecting and outputting the value of correlation of video signals between adjacent frames, an inter-field correlation detecting circuit for detecting and outputting the value of correlation of signals of corresponding pixels between adjacent fields and an adjusting circuit for adjusting the output of the interframe correlation detecting circuit in accordance with the correlation value outputted from the inter-field correlation detecting circuit. There is also disclosed an interlace/non-interlace signal converting circuit which is provided with the motion detecting circuit.
