| 摘要 |
PROBLEM TO BE SOLVED: To solve the problem that illuminating light is vignetted by a picture display element in the case of contriving the miniaturization of a picture display device using a reflection type picture display element. SOLUTION: A light transmission element 3 is provided with at least a 1st surface 8 on which the illuminating light from a light source 1 is made incident, a 2nd surface 10 which emits the illuminating light toward the reflection type picture display element 4 and on which image light from the reflection type picture element is made incident, and a 3rd surface 9 which reflects the illuminating light made incident from the 1st surface toward the 2nd surface and which emits the image light made incident from the 2nd surface toward a projection optical device, and constituted so that an area through which the illuminating light passes and the area through which the image light passes are partially overlapped in the element. When it is assumed that a is an angle formed by the 2nd surface with the 3rd surface of the light transmission element, n is the refractive index of the light transmission element and L is the length [mm] of the side of the reflection type picture display element, tan(ε-α)+tan(ε+α)>; L/12 is satisfied, provided thatε≡sin-1(1/n).
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