In accordance with various embodiments, a radial separation distance between first and second servo seams on a storage medium is determined, and a scaled position signal is generated in relation to the determined radial separation distance and a measured position signal. 04 or less when the projection angle of the image beam onto the center of the holographic screen is set to any angle within a specified projection angle range of 20 to 45, whereby a image display device and holographic screen can be provided wherein the range of the projection angle of the image beam, in which an image with excellent color reproducibility can be displayed, is wide. Moreover, x has a maximum, value adjacent to the anode electrode, and the sum of y and z has a maximum value adjacent to the cathode electrode, while the medium C is an electron injection component comprising either a low work function metal, metal compound, metal alloy, or an organic material with high electron affinity. The second member has a through opening for receiving the extension member. Type information of the POP panel based on a signal output from the detecting elements SW1 to SW3 engaged with the projected and recessed part 33 is output to a display 4.