Provided are a decorative sheet for making the element using external light, for example, a camera or a sensor inconspicuous to an observer and an optical device and an image display device that include the above-described decorative sheet. The decorative sheet including a circularly polarized light reflecting layer, a λ/4 plate A, a linear polarizer, and a λ/4 plate B in this order, in which the circularly polarized light reflecting layer includes one or more cholesteric liquid crystal layers having wavelength selective reflecting properties, in a case where an integral reflectivity at a wavelength λ nm is represented by I-R(λ), I-R(630), I-R(550), and I-R(450) of the circularly polarized light reflecting layer are 30% or higher, and an angle between a slow axis of the λ/4 plate A and an absorption axis of the linear polarizer and an angle between a slow axis of the λ/4 plate B and the absorption axis of the linear polarizer are 45°±10°, respectively.