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. <EOS>