An image decoding apparatus for decoding at least a first coded bit stream into which header information of the H.263 coding scheme and image coded data encoded in the H.263 coding scheme are multiplexed, or for decoding a second coded bit stream into which header information of the MPEG-4 coding scheme and image coded data encoded in the MPEG-4 coding scheme are multiplexed, comprises a switch (102) for switching a decoding analysis scheme of decoding an AC prediction valid/invalid indicator information which indicates whether or not there is an available prediction process for an alternative current component of an intra-coded DCT coefficient according to the received first coded bit stream and the received second coded bit stream.