Offset cancelling circuitry for cancelling offsets among the reference levels of a plurality of video signals each being associated with a particular color. The video signals are each applied to a particular differential amplifier. A multiplexer and a sample and hold circuit multiplex the video signals so as to output the video signal through a single circuit. An analog-to-digital converter converts the multiplexed video signals to corresponding digital data. The color-by-color digital data are each averaged and the resulting mean values are used as correction data. Alternatively, the digital data from the analog-to-digital converter may be transformed to analog data and then fed back to the differential amplifiers as detected and integrated correction data. Further, the multiplexed video signals may be clamped by a clamp buffer circuit and fed back to the differential amplifiers. As a result, offsets among the video signals are cancelled via the sample and hold circuit.