In a light deflection device and a lidar device, a parallel operation can be realized with a simple constitution, so as to avoid enlargement or complication of a system. The reflection angle of the light deflection device depends on a wavelength and a refractive index, so that light beams with respective wavelengths different from each other are simultaneously and parallelly deflected in directions of deflection angles each defined by the wavelength and the refractive index. The light beams with the plural wavelengths different from each other are deflected at the different deflection angles each defined by each wavelength and the refractive index, so that they can be deflected simultaneously and parallelly. The plural deflected light beams can be distinguished from each other based on the difference in the wavelength and the deflection angle of the light, even in the simultaneous and parallel operation.