A load detecting device for detecting whether a load is connected to a power supply device includes a no-load condition detector configured to detect a no-load condition using a sensing voltage having a frequency variant with a switching frequency of the power supply device, a circuit configured to acquire a signal having a waveform differing according to a connection or detachment between the load and the power supply device after the no-load condition is detected by the no-load condition detector, and a detachment detector configured to detect whether the load is detached by sensing the signal acquired by the circuit.