A pitch detection device in which a frequency can be lowered after having maintained both a pitch error accuracy and a response time at practical values to reduce current consumption. Because a number of times of cumulative addition is changed in response to a pitch of a measured signal, a cumulative addition time sum equals or exceeds a constant T_SUM_MIN. Accordingly, a pitch error accuracy of the measured signal achieves a required error accuracy. Furthermore, a frequency of the clock signal is decided using a numerical formula (6) and a numerical formula (7) so that the constant T_SUM_MIN does not exceed a required response time. Accordingly, a response time is within the required response time regardless of whether the frequency of the measured signal is lowered.