An automatic frequency monitoring circuit automatically monitors a frequency of a clock related to an operation of a device to be monitored. In the automatic frequency monitoring circuit, a frequency detecting unit detects, upon detecting a predetermined momentum, the frequencies of a monitoring target clock during a predetermined time for a predetermined number of times and treats as a detection frequency of the monitoring target clock, an average of the frequencies that are detected for the predetermined number of times. A frequency monitoring unit monitors, upon the frequency detecting unit detecting the detection frequency of the monitoring target clock, whether the frequency of the monitoring target clock during the predetermined time is within a predetermined fluctuation range based on the detection frequency.