A multi-layer film, wherein a ratio H/L or L/H, a balance in optical film thickness between a high-refractive-index layer H and a low-refractive-index layer L, is set within a range of 1.2 2.0 to bias a balance in thickness. A method of producing a dielectric multi-layer film, wherein, when a dielectric multi-layer film is formed, a proportion at which an optical film thickness is formed on a monitor substrate is made larger than usual. A UV reflection film, having a step difference in average transmittance of 70 90% at a specified half-power point and within a wavelength range of 430 450 nm, is provided on a substrate to form a UV cut filter. A UV reflection film at a specified half-power point, a step difference in average transmittance of 70 90% within a wavelength range of 430 450 nm, and a blue conditioning film having a transmittance of at least 90% within a wavelength range of 460 520 nm may be combined. This UV cut filter is applied to the projection type display unit of a ultra-high pressure mercury lamp light source. The UV reflection film may be provided on the dustproof glass of a display unit.