A counting device includes a counting unit, period measuring unit, frequency distribution unit, representative value unit, and correction value unit. The counting unit counts signals input during an interval. The signals have a single frequency when the physical quantity is constant. The period measuring unit measures the period of a signal interval. The frequency distribution unit generates the frequency distribution of signal periods from the measurement result. The representative value unit calculates the representative value of the distribution of periods from the frequency distribution. The correction value unit obtains a total sum Ns of frequencies in a class not more than a first predetermined multiple of the representative value and a total sum Nw of frequencies in a class not less than a second predetermined multiple of the representative value from the frequency distribution, and corrects the count result on the basis of the frequencies Ns and Nw.