It is inconvenient for a user that a UI for inputting a virtual focus position at the time of refocus and a UI for inputting a focus position at the time of image capturing exist separately from and independently of each other. An image processing device comprising a generation unit configured to generate combined image data obtained in a case of capturing an image with a second set value different from a first set value used in capturing an image with an image capturing device by using a plurality of pieces of captured image data obtained by the image capturing device, wherein the image capturing device is capable of capturing image data from a plurality of viewpoint positions and includes an operation unit for setting a set value of an image capturing parameter, and wherein the first and second set values are set via the operation unit.