An image decoding apparatus and an image decoding method capable of generating a decoded image even in the case where a pixel in a block is necessary as a reference pixel, the block where an intra prediction mode specified in a stream is unavailable according to a standard, due to a transmission error, a coding-method error, or the like. An image decoding apparatus (200) determines whether or not a reference block necessary for a specified intra prediction mode is available, based on intra-prediction mode information extracted by an intra-prediction mode extraction unit (102) and peripheral block pixel information stored in a line memory (104). The image decoding apparatus (200) includes a reference pixel determination unit (201) which controls a switch unit (202); and a substitute intra-prediction image generation unit (203) which generates a substitute intra-prediction image in the case where a reference block necessary for a specified intra prediction mode is unavailable.