There was a problem that it was difficult for a semiconductor device in the related art to increase the switching frequency of a step-up circuit, and it was difficult to stabilize an output current and an output voltage. A semiconductor device controls a step-up circuit including an inductor and a drive transistor to drive the inductor. The semiconductor device calculates upper and lower limits which determine the variable range of an input current, based on an output current and an input voltage, controls the switch timing of the drive transistor based on the relation between the upper and lower limits and the magnitude of the input current, and at the same time, corrects the upper and lower limits to be calculated, based on the magnitude of the difference between the output current and a target output current value as an ideal value of the output current.