A coded code string from an input terminal 110 is demultiplexed by a demultiplexer circuit 101, normalization coefficient information in the code string is sent to a normalization coefficient information increasing/decreasing circuit 102, addition or subtraction of a positive value is performed, and level adjustment of a signal is performed. A normalization coefficient information cutoff amount calculating circuit 103 calculates the cutoff amount for a case where the subtraction amount of normalization coefficient information is larger than normalization coefficient information and normalization coefficient information after subtraction is cut off at the minimum possible value. A gain control function generation information modifying circuit 104 modifies gain control function generation information according to the cutoff amount.