A light modulation device comprising an active liquid crystal film layer having first and second polymer film substrates (11, 13) disposed opposite to each other, and an active liquid crystal layer which is present between the polymer film substrates (11, 13) and contains a liquid crystal host and a dichroic dye guest, wherein the active liquid crystal layer can switch between a horizontal orientation state and a vertical orientation state, wherein each of the polymer film substrates (11, 13) has an in-plane retardation of 4,000 nm or more for light having a wavelength of 550 nm, wherein each of the first polymer film substrate and the second polymer film substrate is a stretched polymer film, wherein a respective first direction of the first polymer film substrate and the second polymer film substrate is an in-plane transverse direction and a respective second direction of the first polymer film substrate and the second polymer film substrate is an in-plane machine direction, characterized in that the in-plane transverse direction is a respective slow axis direction, and the in-plane machine direction is a respective fast axis direction, wherein each of the first polymer film substrate and the second polymer film substrate has a ratio (E1/E2) of an elongation in the first direction to an elongation in the second direction perpendicular to the first direction of 3 or more, the first polymer film substrate and the second polymer film substrate are disposed so that an angle formed by the first direction of the first polymer film substrate and the first direction of the second polymer film substrate is in a range of o degrees to 10 degrees, wherein the elongation is measured by conducting a tensile strength test by applying a force at a tensile speed of 10 mm/min at room temperature (25°C) and specimen for measuring the elongation has a width of 10 mm and a length 30 mm. wherein the active liquid crystal layer can switch between a horizontal orientation state and a vertical orientation state, wherein each of the polymer film substrates (11, 13) has an in-plane retardation of 4,000 nm or more for light having a wavelength of 550 nm, wherein each of the first polymer film substrate and the second polymer film substrate is a stretched polymer film, wherein a respective first direction of the first polymer film substrate and the second polymer film substrate is an in-plane transverse direction and a respective second direction of the first polymer film substrate and the second polymer film substrate is an in-plane machine direction, characterized in that the in-plane transverse direction is a respective slow axis direction, and the in-plane machine direction is a respective fast axis direction, wherein each of the first polymer film substrate and the second polymer film substrate has a ratio (E1/E2) of an elongation in the first direction to an elongation in the second direction perpendicular to the first direction of 3 or more, the first polymer film substrate and the second polymer film substrate are disposed so that an angle formed by the first direction of the first polymer film substrate and the first direction of the second polymer film substrate is in a range of o degrees to 10 degrees, wherein the elongation is measured by conducting a tensile strength test by applying a force at a tensile speed of 10 mm/min at room temperature (25°C) and specimen for measuring the elongation has a width of 10 mm and a length 30 mm.