There are disclosed a watermark information embedment device capable of accurately embedding secret information, and a watermark information detection device. In the watermark information embedment device, there are prepared a plurality of different sorts of dot patterns in which the wave propagation direction and the wave length are changed depending on the dot arrangement. Each dot pattern of the same sort is given the same symbol, and the secret information is represented by combining these dot patterns. In the watermark information detection device, there are provided 2-dimensional wavelet filters having the same wave propagation direction and the wave length as the different sorts of dot patterns. There is computed convolution between an arbitrary region in the watermarked image and plural 2-dimensional wavelet filters, and it is judged that the dot pattern corresponding to a particular one of the 2-dimensional wavelet filters is embedded in the region where the computed convolution indicates a maximum value.