A switching power supply apparatus, including: a switching device (Tr1, Tr2) for performing an on/off operation; a control circuit for controlling on/off of the switching device; a coil, a level of a current flowing therethrough being controlled by the switching device; a capacitor that is connected to the coil and that performs rectification together with the coil; and an oscillator for outputting to the control circuit an oscillating signal at intervals of a fixed time period for turning the switching device on, wherein the switching power supply apparatus outputs an output voltage from a node at which the capacitor and the coil are connected together, the switching power supply apparatus comprising: a current detection portion for detecting a current value flowing through the coil, converting the detected current value into a voltage value relative to a supply potential (Vcc), and then outputting the voltage value thus obtained as a current detection voltage; a voltage source for adding a direct-current offset voltage (Voff) to the current detection voltage from the current detection portion; a differential amplifier for amplifying a difference between a voltage commensurate with the output voltage and a reference voltage; a level shifter for shifting a level of the voltage outputted from the differential amplifier to a supply potential (Vcc) side; and a comparator for comparing the current detection voltage to which the offset voltage (Voff) is added by the voltage source with a voltage (Vth) outputted from the level shifter, wherein the offset voltage (Voff) falls within the voltage range in which, when a heavy load is connected, the influence thereof on the voltage inputted to the comparator is so small that it can be ignored, wherein, if the comparator finds the current detection voltage to which the offset voltage is added to be greater than the voltage (Vth) outputted from the level shifter, the oscillating signal from the oscillator is masked, and the switching device is turned off. a switching device (Tr1, Tr2) for performing an on/off operation; a control circuit for controlling on/off of the switching device; a coil, a level of a current flowing therethrough being controlled by the switching device; a capacitor that is connected to the coil and that performs rectification together with the coil; and an oscillator for outputting to the control circuit an oscillating signal at intervals of a fixed time period for turning the switching device on, wherein the switching power supply apparatus outputs an output voltage from a node at which the capacitor and the coil are connected together, the switching power supply apparatus comprising: a current detection portion for detecting a current value flowing through the coil, converting the detected current value into a voltage value relative to a supply potential (Vcc), and then outputting the voltage value thus obtained as a current detection voltage; a current detection portion for detecting a current value flowing through the coil, converting the detected current value into a voltage value relative to a supply potential (Vcc), and then outputting the voltage value thus obtained as a current detection voltage; a voltage source for adding a direct-current offset voltage (Voff) to the current detection voltage from the current detection portion; a differential amplifier for amplifying a difference between a voltage commensurate with the output voltage and a reference voltage; a level shifter for shifting a level of the voltage outputted from the differential amplifier to a supply potential (Vcc) side; and a comparator for comparing the current detection voltage to which the offset voltage (Voff) is added by the voltage source with a voltage (Vth) outputted from the level shifter, wherein the offset voltage (Voff) falls within the voltage range in which, when a heavy load is connected, the influence thereof on the voltage inputted to the comparator is so small that it can be ignored, wherein, if the comparator finds the current detection voltage to which the offset voltage is added to be greater than the voltage (Vth) outputted from the level shifter, the oscillating signal from the oscillator is masked, and the switching device is turned off.