An object of the present invention is to provide a retardation film excellent in various properties such as optical properties, heat resistance, mechanical properties, and reliability. The present invention relates to a retardation film containing a thermoplastic resin and composed of a single layer, in which the retardation film has a value of wavelength dispersion that is a ratio of retardations at a wavelength of 450 nm and at a wavelength of 550 nm being 0.75 or more and 0.92 or less; a birefringence at a wavelength of 550 nm and the wavelength dispersion satisfy a relationship of Δn≥0.0140×(R450/R550)−0.0082; and a photoelastic coefficient is 25×10−12 Pa−1 or less.