A device for controlling the table capacity smaller comprises a table of logarithms and a table of exponents preserving values of a logarithmic function and exponential function with a base of the second power, a multiplier, a shift unit for shifting the input value by a proper integer when the domain of logarithm is not included in the input value range of the table of logarithms, a logarithm addition unit for adding the shift amount to the value referred to in the table of logarithms, an exponent subtraction unit for subtracting a proper integer L from the input value when the domain of the exponential function is not included in the input value range of the table of exponents, and an exponent shift unit for shifting the referred value in the table of exponents the subtraction amount. A high-speed processing unit comprises a converter for converting floating-point data to fixed-point data having a bit of decimal point. By doing this, a structured graphics system can perform high-speed processing with a small table capacity.