The multimedia data decoder includes a decoding section and a control section. The decoding section for decoding coded data in a bit stream has a function to detect a synchronous word from the bit stream, analyze decoding information following the synchronous word and extract specific option designating information from the decoding information. The control section determines whether or not the option designating information extracted by the decoding section has any out-of-standard value, that is, any value that is not defined by a standard. If the option designating information has any out-of-standard data, the control section controls the decoding section so as to replace the out-of-standard value with a value defined by the standard and conduct a decoding process. For this purpose, the control section applies replacement information to the decoding section. Accordingly, decoded data is obtained even if the decoding information has an out-of-standard value.