1. An electronic watermark embedding device for embedding classified information in a document image by watermarking comprising: a watermark image forming section for creating a watermark image based on the classified information while referring to the document image, wherein the watermark image forming section calculates an embedding region for embedding a dot pattern in which a prescribed symbol can be identified by a prescribed filter, and determines whether or not the proportion of text region to the embedding region is less than or equal to a prescribed threshold value, for the document image, and if the proportion of the document region is less than or equal to the prescribed threshold value, a prescribed number of dot patterns (symbol units) in which a symbol formed of at least a portion of the classified information is identifiable, is embedded in a region where the embedding region and the text region do not overlap.