In an A/D converting apparatus, a converting unit has an input terminal and an input-output characteristic. The input-output characteristic has temperature dependence, and the converting unit carries out a process of converting an input voltage signal to digital data. A temperature determining unit has information representing a relationship between a variable of an output of the converting unit and a variable of a temperature around the converting unit according to the temperature dependence of the input-output characteristic of the converting unit. When the specified voltage is applied to the input terminal of the converting unit, the temperature determining unit determines a value of the temperature around the converting unit based on the information and the specified voltage. A reducing unit reduces temperature dependence of the process of converting an input voltage signal to digital data based on the determined value of the temperature around the converting unit.