In order to provide a highly precise analog/digital conversion system in which an output error of an AD converter is small, sampling is performed at a certain sampling period S from the start time of a measurement period TL to the (N−1)-th sampling when the measurement period TL does not correspond to the sampling period S multiplied by the number of samplings N, the N-th sampling is performed at a timing when a time interval between the (N−1)-th sampling and the N-th sampling is equal to the sampling period S multiplied by a predetermined coefficient k, and the k value is set to a non-integer optimum value evaluated in advance in accordance with the N value in order to minimize an error of the detection value of the AD converter.
