In a DC-to-DC converter control circuit and control method thereof, an arithmetic circuit for outputs an add-up signal generated by adding an output voltage signal obtained by adding an output voltage of a DC-to-DC converter and an AC current signal obtained according to an AC current component of a coil current, and a comparator compares the add-up signal with a reference signal. Switching control is executed according to a result of the comparison by the comparator. By the control circuit and method, variations in the coil current due to a change in load may be reliably captured by comparing the add-up signal with the reference signal, and compatibility between low ripple voltage characteristics and stable and fast response to sudden changes in load may be achieved.