Abstract: A power-off detection device is formed without use of a photo coupler, which is expensive and occupies a relatively large area. The power-off detection device rectifies AC power, provided as external input power from a power supply device, into DC power, detects the power-off of the external input power from the power supply device as provided to an electronic appliance, provides a power-off detection signal to central control means of the electronic appliance, and enables the central control means to prepare for the power-off, thereby reducing manufacturing cost of the power supply device, and achieving miniaturization thereof.