In an image encryption apparatus, each of pixel-value inverse-converters applies pixel-value inverse-conversion on an input image in each of previously-encrypted areas. An image combiner superimposes images with inversely-converted pixels in the previously-encrypted areas to the input image to obtain a ready-to-encrypt image. An image encryptor scrambles blocks in the ready-to-encrypt image. A pixel-value converter applies pixel-value conversion on each of scrambled blocks to obtain a multiply-encrypted image. In an image decryption apparatus, a pixel-value inverse-converter applies pixel-value inverse-conversion on each scrambled block in the multiply-encrypted image to obtain a dot-erased image. An image decryptor inversely scrambles the scrambled blocks in the dot-erased image to obtain a decrypted image. Each of pixel-value converters applies pixel-value conversion on the decrypted image in each of previously-encrypted areas. An image combiner superimposes images with converted pixels in the previously-encrypted areas to the decrypted image to obtain a previously-encrypted image.