Disclosed is an illuminating device which has: a first illuminating lamp which is disposed at a first predetermined position and is identifiable; a second illuminating lamp which is disposed at a second predetermined position having a predetermined relationship with the first predetermined position and is identifiable; a determining means which determines the mutual relationship between the first illuminating lamp and the second illuminating lamp; and a transmitting means which transmits identifiable control signals to the first illuminating lamp and the second illuminating lamp, respectively, so as to achieve the determination made by the determining means.