An optical device having exactly one substrate; a first polarizing layer disposed adjacent to said substrate; and a liquid crystal window which is present on a surface of said first polarizing layer opposite to another surface of said first polarizing layer on which the substrate is located and comprises a liquid crystal layer having a liquid crystal compound, wherein the optical device is configured such that transmittance varies depending on whether or not an electric field is applied to the liquid crystal layer, wherein: - the liquid crystal window further comprises only one base layer that is present on a surface of the liquid crystal layer opposite to another surface of the liquid crystal layer on which the first polarizing layer is located, a first electrode layer which is in direct contact with the first polarizing layer, a second electrode layer which is in direct contact with the base layer, a first alignment film which is in direct contact with the first electrode layer and a second alignment film which is in direct contact with the second electrode layer, wherein the first polarizing layer is in direct contact with the liquid crystal window, wherein the opposite side of the surface that is in contact with the liquid crystal window of the first polarizing layer is attached to the substrate via a pressure-sensitive adhesive layer or an adhesive layer, and wherein the base layer has a coefficient of thermal expansion of 50 ppm/K to 300 ppm/K and an elastic modulus of 0.5 GPa to 5 GPa. a first polarizing layer disposed adjacent to said substrate; and a liquid crystal window which is present on a surface of said first polarizing layer opposite to another surface of said first polarizing layer on which the substrate is located and comprises a liquid crystal layer having a liquid crystal compound, wherein the optical device is configured such that transmittance varies depending on whether or not an electric field is applied to the liquid crystal layer, wherein: - the liquid crystal window further comprises only one base layer that is present on a surface of the liquid crystal layer opposite to another surface of the liquid crystal layer on which the first polarizing layer is located, a first electrode layer which is in direct contact with the first polarizing layer, a second electrode layer which is in direct contact with the base layer, a first alignment film which is in direct contact with the first electrode layer and a second alignment film which is in direct contact with the second electrode layer, - the liquid crystal window further comprises only one base layer that is present on a surface of the liquid crystal layer opposite to another surface of the liquid crystal layer on which the first polarizing layer is located, a first electrode layer which is in direct contact with the first polarizing layer, a second electrode layer which is in direct contact with the base layer, a first alignment film which is in direct contact with the first electrode layer and a second alignment film which is in direct contact with the second electrode layer, wherein the first polarizing layer is in direct contact with the liquid crystal window, wherein the opposite side of the surface that is in contact with the liquid crystal window of the first polarizing layer is attached to the substrate via a pressure-sensitive adhesive layer or an adhesive layer, and wherein the base layer has a coefficient of thermal expansion of 50 ppm/K to 300 ppm/K and an elastic modulus of 0.5 GPa to 5 GPa.