Provided are a reflection film, which enables high visible light transmittance, an increase in the brightness of a display image, and favorable transparency of an external tint, a windshield glass, and a head-up display system. The reflection film includes a selective reflection layer formed of a cholesteric liquid crystal layer with a cholesteric liquid crystalline phase immobilized. In each of a wavelength range of 400 nm or more and less than 500 nm and a wavelength range of 500 nm or more and less than 600 nm, a maximum value of a natural light reflectivity is 10% to 25%, the greatest difference between the greatest maximum value and the smallest minimum value of the natural light reflectivity is 3% or more, and a total value of wavelength bandwidths in a region where a reflectivity is higher than an average value of the maximum value and the minimum value of the natural light reflectivity is 20 nm to 80 nm. In a wavelength range of 600 nm or more and 800 nm or less, a maximum value of a natural light reflectivity is 10% to 25%, and a total value of wavelength bandwidths in a region where a reflectivity is higher than an average value of the maximum value and the minimum value of the natural light reflectivity is 120 nm or more.