Abstract: A device for determining quantizing number of an image signal comprises a discrete cosine transformation for generating a discrete cosine transformation signal by transforming image data, a segment delay unit for delaying the discrete cosine transformation signal for prescribed time, a quantization unit for quantizing data output from the segment delay unit, a variable coding unit for variably coding data output from the quantizing unit, a formatter for converting data output from the variable coding unit into an appropriate form, an activity calculation unit for counting a number of a discrete cosine transformation signal in a macro block unit and for calculating activity, a target bit calculation unit for calculating a target bit based on the data output from the activity calculation unit, a code length calculation unit for calculating quantizing and a code length of said discrete cosine transformation signal, the code length calculation unit quantizing and variably coding the discrete cosine transformation