Transmissive liquid crystal diffraction element

A transmissive liquid crystal diffraction element comprising:

• a first optically-anisotropic layer and a second optically-anisotropic layer each of which has a liquid crystal alignment pattern in which an orientation of an optical axis derived from a liquid crystal compound changes while continuously rotating in at least one in-plane direction;
• and two retardation layers that are disposed on a side of the second optically-anisotropic layer opposite to the first optically-anisotropic layer and between the first optically-anisotropic layer and the second optically-anisotropic layer, respectively, wherein a rotation direction of the optical axis in the liquid crystal alignment pattern of the first optically-anisotropic layer and a rotation direction of the optical axis in the liquid crystal alignment pattern of the second optically-anisotropic layer are opposite to each other;
• wherein a length over which the orientation of the optical axis derived from the liquid crystal compound in the liquid crystal alignment pattern rotates by 180° in a plane is set as a single period, a single period Λ1 of the liquid crystal alignment pattern in the first optically-anisotropic layer and a single period Λ2 of the liquid crystal alignment pattern in the second optically-anisotropic layer satisfy Λ1/Λ2=0.2 to 5, the retardation layer is a positive C-plate or an O-plate, and the positive C-plate satisfies Expression (1), 0.12≤|Rth(λ)/λ|≤0.66 . . . (1), where λ represents a wavelength (nm) of incidence light, and Rth(λ) represents a retardation (nm) in a thickness direction at the wavelength λ nm of the retardation layer).