PURPOSE: To simplify the decoding processing and to attain high speed processing by adding a fixed data with a fixed length to a head of a coding data inputted to a decoding table so as to distinguish a high-order invalid data and a low-order valid data of the decoding object data.

CONSTITUTION: Since a fixed data '1' is set to the least significant bit as a decoding object data, a detection flag 4 is naturally '0' and an event 5 has no meaning. Then in the processing step 2, a succeeding bit data '0' of a coding data 2 is inputted and a low-order bit is recognized as a valid data from the fixed data (first '1' from the most significant digit) in a decoding table 1 and the detection flag 4 is outputted. Then in the processing step 3, similarly to the processing step 2, a succeeding bit data '0' of the coding data 2 is inputted. Then in the processing step 4, a succeeding bit data '1' of the coding data 2 is inputted and a valid data '001' is recognized similarly. The detection flag 4 is '1' and when a CPU detects it, an event 5 is read and the decoding of an event (c) is recognized.