White polyester film and the reflection sheet

【Task】 The present invention, the conventional view of the problems of the technology, in which high reflectivity and is both a high hiding property, and aims to film breakage provides a high white polyester film productivity hardly generated. A In the white polyester film containing voids therein, a layer of resin constituting the film is formed by using a polyester resin and a cyclic olefin copolymerized resin, and a cavity ratio in the layer cross section 75% or less over 25% by and number average particle diameter of the cyclic olefin copolymerized resin in the film can be achieved by at 0.1μm or more 3μm or less. .BACKGROUND