Backlight unit and liquid crystal display device

Display performance can be improved by reducing light leak in an oblique direction at the time of black display while increasing front brightness. Provided is a backlight unit including: a light collimating member in which a lens array is formed on one surface of a transparent substrate and a plurality of truncated cones are arranged on another surface of the transparent substrate; a light guide plate; and a light source, in which the truncated cone on the light collimating member has a shape in which a width decreases away from the transparent substrate in a height direction, a position of each of lenses of the lens array deviates from a position of the truncated cone corresponding to the lens to move away from the light source in a direction that connects a center of the lens and the light source most adjacent to the lens, an optical axis of the lens is arranged to pass through a slope of the truncated cone corresponding to the lens, the light guide plate and a surface of the truncated cone opposite to the transparent substrate are in contact with each other, and the shape of the truncated cone of the light collimating member satisfies specific expressions.