An image pickup apparatus able to reliably detect a power supply abnormality even in an arrangement in which power supplies are managed by using a communication unit of single system. The image pickup apparatus includes a recording unit for writing image data onto a recording medium, and a power supply control unit for selecting and executing either a monitoring operation to monitor a state of a power supply for a camera main unit or a communication operation to communicate with a power supply for an accessory unit. The power supply control unit selects and executes the monitoring operation while the recording unit is performing an image data writing operation.