A voltage variation detection circuit comprising: a threshold voltage generation circuit (1, 2A, 2B, 3) configured to generate a first threshold voltage; a first comparator configured to compare a variation detection-target voltage and the first threshold voltage to each other; and a controller configured to control the threshold voltage generation circuit based on output of the first comparator and output of the second comparator, characterized in that the threshold voltage generation circuit is configured to further generate a second threshold voltage lower than the first threshold voltage, the voltage variation detection circuit further comprises a second comparator configured to compare the variation detection-target voltage and the second threshold voltage to each other, the controller is configured to control the threshold voltage generation circuit in such fashion that the threshold voltage generation circuit repeats operations of: decreasing the first threshold voltage stepwise and increasing the second threshold voltage stepwise; when the variation detection-target voltage has come to the first threshold voltage or more or to the second threshold voltage or less, first increasing the first threshold voltage by specified steps and decreasing the second threshold voltage by specified steps and then again decreasing the first threshold voltage stepwise and increasing the second threshold voltage stepwise; and when the variation detection-target voltage has come to the threshold voltage or more or to the second threshold voltage or less, increasing the first threshold voltage by specified steps and decreasing the second threshold voltage by specified steps, and the controller is configured to detect a variation of the variation detection-target voltage based on a value of the first threshold voltage at the time point when the variation detection-target voltage comes to the first threshold voltage or more or a value of the second threshold voltage at the time point when the variation detection-target voltage comes to the second threshold voltage or less. a threshold voltage generation circuit (1, 2A, 2B, 3) configured to generate a first threshold voltage; a first comparator configured to compare a variation detection-target voltage and the first threshold voltage to each other; and a controller configured to control the threshold voltage generation circuit based on output of the first comparator and output of the second comparator, characterized in that the threshold voltage generation circuit is configured to further generate a second threshold voltage lower than the first threshold voltage, the voltage variation detection circuit further comprises a second comparator configured to compare the variation detection-target voltage and the second threshold voltage to each other, the controller is configured to control the threshold voltage generation circuit in such fashion that the threshold voltage generation circuit repeats operations of: decreasing the first threshold voltage stepwise and increasing the second threshold voltage stepwise; when the variation detection-target voltage has come to the first threshold voltage or more or to the second threshold voltage or less, first increasing the first threshold voltage by specified steps and decreasing the second threshold voltage by specified steps and then again decreasing the first threshold voltage stepwise and increasing the second threshold voltage stepwise; and when the variation detection-target voltage has come to the threshold voltage or more or to the second threshold voltage or less, increasing the first threshold voltage by specified steps and decreasing the second threshold voltage by specified steps, and the controller is configured to detect a variation of the variation detection-target voltage based on a value of the first threshold voltage at the time point when the variation detection-target voltage comes to the first threshold voltage or more or a value of the second threshold voltage at the time point when the variation detection-target voltage comes to the second threshold voltage or less. a value of the first threshold voltage at the time point when the variation detection-target voltage comes to the first threshold voltage or more or a value of the second threshold voltage at the time point when the variation detection-target voltage comes to the second threshold voltage or less.