1. A device for determining a principal facial image in a captured image, the device comprising: one or more processors; a facial image grouping device for grouping multiple facial images obtained from multiple captured images by event to generate a plurality of facial image groups; a principal facial image determination device for determining one or a plurality of principal facial images of facial images included in each of the plurality of facial image groups generated by the facial image grouping device as a facial image of a principal person of the multiple captured images for each facial image group; and a facial image group mixing device for assembling facial image groups, in which the number of facial images included in each of the plurality of facial image groups generated by the facial image grouping device is less than a given number, in one facial image group, wherein the principal facial image determination device determines the facial image group assembled in said facial image group mixing device and a principal facial image of facial images included in each of the plurality of facial image groups generated by said facial image grouping device as a facial image of a principal person of the multiple captured images for each facial image group.