A characteristic amount is retained and calculated from an entered video signal. Embedment intensity is retained and calculated from the retained characteristic amount. Embedment information is embedded as digital watermarks into the entered video signal in accordance with the retained embedment intensity of the previous frame or field that is located at a position earlier in time than a target image subject to digital watermark embedment. As a result, an output signal of video having the digital watermarks embedded therein is produced. The digital watermarks are embedded into the target image with reference to another image located at a position earlier in time than the target image. Such digital watermark embedment suppresses a delay in output of an output image with reference to an input image.