Provided are an optical element and a concentrating photovoltaic device which are each capable of preventing warpage and deformation of an optical functional pattern formed in a surface thereof due to stress even in an environment with extreme temperature changes. An optical element (4) of a concentrating photovoltaic device (1) concentrating sunlight includes: a glass substrate (5) and a sheet-like molded body (6) which is made of an organic resin and includes a Fresnel lens pattern (6a) in a surface and has the other surface bonded to the glass substrate (5). The sheet-like molded body (6) has a tensile elastic modulus of 1500 MPa or less, a linear expansion coefficient of 7.0×10−5/° C. or less, an average transmittance of 85% or more in a wavelength range from 350 to 1850 nm at a thickness of 400 μm, and a haze value of 1.0% or less.