To provide a simply-structured image decoding apparatus which appropriately executes parallel decoding processing.The image decoding apparatus includes: a stream segmentation unit (130) which generates four segment streams by segmenting each of the pictures included in a bit stream into plural MB lines, and assigning each of the plural MB lines to a corresponding one of the four segment streams to be generated; and four decoding engines (120) which decode the respective four segment streams in parallel. When the stream segmentation unit (130) segments a slice in the picture into slice portions and assigns the respective slice portions to plural segment streams, the stream segmentation unit (130) reconstructs, as a new slice, the slice portion group including at least one slice portion to be assigned to a corresponding one of the segment streams so that the slice portion group is recognized as a slice by the associated one of the decoding engines (120).