An image pickup apparatus, an external device and an image pickup method enabling provision of an open area in an image memory by performing automatic transfer operation of a digital image signal without requiring a user to cancel a photography preparation instruction or a picture taking instruction are provided. A digital camera or the image pickup apparatus is arranged to transfer to a computer a digital image signal accumulated in a RAM when the digital camera is in a photography preparation state or in a photography execution state, when an image already saved to a storage medium exists in the RAM, and when the RAM is full and a new digital image signal cannot be accumulated.