A switching power supply device comprising: a switching circuit configured to convert DC power supplied from a DC power supply into AC power; a rectifier circuit including a plurality of rectifier elements (Q5, Q6) configured to rectify the AC power resulting from conversion by the switching circuit ; a snubber circuit including a power storage element (C) configured to store therein surge power due to a reverse recovery time of the rectifier elements (Q5, Q6), a switching element (Q7) configured to discharge the surge power stored in the power storage element (C), and an inductor provided in a stage following the switching element (Q7); and a controller configured to control an on-duty (D2) at which the switching element (Q7) is turned on based on the surge power, characterized in that the snubber circuit has a continuous current mode in which an electric current flowing through the inductor continuously flows and a discontinuous current mode in which the electric current flowing through the inductor discontinuously flows; the controller is configured to set the on-duty (D2) of the switching element (Q7) to a constant value (D max ) in the continuous current mode, the controller is configured to control the switching element (Q7) at a preset lower limit (Dth) indicating a lower limit of the on-duty (D2), in the discontinuous current mode only, the on-duty lower limit (Dth) is smaller than the constant on-duty value (D max ) set for the switching element (Q7) in the continuous current mode and larger than 0, the on-duty lower limit (Dth) is equal to or larger than the on-duty (D2) of the switching element (Q7) capable of outputting a snubber current minimum value (α) serving as a minimum value of an electric current output from the snubber circuit , and when the on-duty (D2) at which the switching element (Q7) is turned on based on the surge power is smaller than the on-duty lower limit (Dth), the controller turns on the switching element (Q7) at the on-duty lower limit (Dth). a switching circuit configured to convert DC power supplied from a DC power supply into AC power; a rectifier circuit including a plurality of rectifier elements (Q5, Q6) configured to rectify the AC power resulting from conversion by the switching circuit ; a snubber circuit including a power storage element (C) configured to store therein surge power due to a reverse recovery time of the rectifier elements (Q5, Q6), a switching element (Q7) configured to discharge the surge power stored in the power storage element (C), and an inductor provided in a stage following the switching element (Q7); and a controller configured to control an on-duty (D2) at which the switching element (Q7) is turned on based on the surge power, characterized in that the snubber circuit has a continuous current mode in which an electric current flowing through the inductor continuously flows and a discontinuous current mode in which the electric current flowing through the inductor discontinuously flows; the controller is configured to set the on-duty (D2) of the switching element (Q7) to a constant value (D max ) in the continuous current mode, the controller is configured to control the switching element (Q7) at a preset lower limit (Dth) indicating a lower limit of the on-duty (D2), in the discontinuous current mode only, the on-duty lower limit (Dth) is smaller than the constant on-duty value (D max ) set for the switching element (Q7) in the continuous current mode and larger than 0, the on-duty lower limit (Dth) is equal to or larger than the on-duty (D2) of the switching element (Q7) capable of outputting a snubber current minimum value (α) serving as a minimum value of an electric current output from the snubber circuit , and when the on-duty (D2) at which the switching element (Q7) is turned on based on the surge power is smaller than the on-duty lower limit (Dth), the controller turns on the switching element (Q7) at the on-duty lower limit (Dth). <EOS>