Precision of arithmetic operations on floating-point numbers is improved while also preventing an increase in the amount of processing. A second converter converts an exponent included in an exponent field according to an exponent conversion rule defined in accordance with a function. A storage stores in a table a value obtained by converting a mantissa field according to a mantissa conversion rule defined in accordance with the function. A retrieving unit derives an index of the table, by extracting the most significant 8 bits from the 23 bits constituting the mantissa field. The retrieving unit adds 1 to the mantissa field approximated by the most significant 8 bits so as to derive a second index. A deriving unit derives a tentative return value A and a tentative return value B. Further, the deriving unit interpolates between the tentative return value A and the tentative return value B so as to derive a return value of the function.