A computation apparatus includes an inverse conversion table creation unit configured to create an inverse conversion table in which discrete values obtained by applying a predetermined conversion on predetermined data correspond to inverse conversion values obtained by applying a conversion inverse to the predetermined conversion on the discrete values, a range decision unit configured to decide in which range the predetermined data is included when the predetermined data is input among ranges where the inverse conversion values adjacent in the inverse conversion table are set as border values, and a discrete value decision unit configured to decide the discrete value corresponding to the inverse conversion value whose value is close to the predetermined data among the inverse conversion values serving as the border values of the range decided by the range decision unit.