The invention provides a switching power supply device that can restrain the variation in the ripple of the output voltage corresponding to the variation in the input voltage and a control device thereof. When output voltage Vout is higher than a target value, switching converter circuit 10 is set to a second state (a state of discharging the power stored in inductor L1 to terminal To). When output voltage Vout is lower than the target value, switching converter circuit 10 is set to a first state (a state of storing the power input from terminal Ti in inductor L1) for a prescribed period of time and is then returned to the second state. Also, when the current flowing through inductor L1 exceeds a threshold value, switching converter circuit 10 is set to the second state. In addition, the threshold value of the inductor current is adjusted corresponding to the ratio between input voltage Vin and output voltage Vout, so that the variation in the ripple of output voltage Vout occurring together with the variation in that ratio can be restrained.