1. An electronic watermark embedding method comprising: a dividing processing step of dividing an electronic image into which an electronic watermark is to be embedded into a plurality of image regions spatially; an adaptive extraction step of extracting, as adaptive pixels, pixels each having a property of being difficult to visually recognize a variation in a pixel value from each of said plurality of image regions; and an embedding step of producing a variation between the pixel values of said adaptive pixels in one of said plurality of image regions and those of said adaptive pixels in an adjacent one of said plurality of image regions, and varying the pixel values of said adaptive pixels of said plurality of image regions in a time direction, according to a value of an embedded bit set of an electronic watermark, and of generating an electronic-watermark-embedded image by making the variation in the pixel values of said adaptive pixels vary step by step at a boundary between the two of said plurality of image regions and/or in the time direction so that the variation makes a slow transition.