A picture decoding method and apparatus for decoding a bit stream, the bit stream being compatible with MPEG 1 moving picture video standard. The method includes receiving, via an input terminal, from a bit stream that includes extension data added in a header of a picture layer of the bit stream when the header includes control data that is newly added in MPEG 2 standard format, the extension data of an anterior header of the picture layer. The method also includes decoding the bit stream in the picture layer using the extension data of an anterior header of the picture layer when an extension start code indicating the beginning of the extension data of the current header is not received from the bit stream.