A switching power supply circuit control method for controlling a switching power supply circuit, wherein said switching power supply circuit includes: first and second input terminals (P1, P2); first and second output terminals (P3, P4) to which a capacitor and a load are connected; a second power supply line connecting said second input terminal and said second output terminal; and one or more circuits (3a, 3b), each of said one or more circuits (3a, 3b) includes: a first power supply line (LH1, LH2) connecting said first input terminal and said first output terminal; a reactor (L1, L2) provided on said first power supply line (LH1, LH2); a diode (D11, D21) connected in series to said reactor (L1, L2) on said first power supply line (LH1, LH2), and positioned such that an anode thereof is directed toward said reactor (L1, L2); and a switch element (S1, S2) provided between said second power supply line and a point between said reactor (L1, L2) and said diode (D11, D21), said switching power supply circuit control method being characterized by comprising the steps of: making said switch element (S1, S2) of each of said one or more circuits nonconductive when power consumption of said load is smaller than a first threshold (P11; P12; P13; P14; P15; P16; P21; P22) to supply power from all of said one or more circuits to said load while adopting a nonconductive mode as current mode, and making said switch element of at least one of said one or more circuits (3a, 3b) intermittently conductive when said power consumption of said load is larger than said first threshold to supply power from all of said one or more circuits (3a, 3b) to said load while adopting one of a discontinuous mode, a critical mode, and a continuous mode as current mode; switching the current mode of at least one of said one or more circuits (3a, 3b) depending on the magnitude of output of the switching power supply circuit so as to maintain the leakage current lower than a threshold. first and second input terminals (P1, P2); first and second output terminals (P3, P4) to which a capacitor and a load are connected; a second power supply line connecting said second input terminal and said second output terminal; and one or more circuits (3a, 3b), a first power supply line (LH1, LH2) connecting said first input terminal and said first output terminal; a reactor (L1, L2) provided on said first power supply line (LH1, LH2); a diode (D11, D21) connected in series to said reactor (L1, L2) on said first power supply line (LH1, LH2), and positioned such that an anode thereof is directed toward said reactor (L1, L2); and a switch element (S1, S2) provided between said second power supply line and a point between said reactor (L1, L2) and said diode (D11, D21), making said switch element (S1, S2) of each of said one or more circuits nonconductive when power consumption of said load is smaller than a first threshold (P11; P12; P13; P14; P15; P16; P21; P22) to supply power from all of said one or more circuits to said load while adopting a nonconductive mode as current mode, and making said switch element of at least one of said one or more circuits (3a, 3b) intermittently conductive when said power consumption of said load is larger than said first threshold to supply power from all of said one or more circuits (3a, 3b) to said load while adopting one of a discontinuous mode, a critical mode, and a continuous mode as current mode; switching the current mode of at least one of said one or more circuits (3a, 3b) depending on the magnitude of output of the switching power supply circuit so as to maintain the leakage current lower than a threshold.