1. A retroreflectometer giving direct readings, for measuring the value or degree of retroreflectivity of a paint applied to the road surface for marking road signs, and consisting essentially of a light-proof box or chamber (1), essentially prismatic in shape, and having in its under-side a rectangular opening or "window" (2) the perimeter of which has a frame (3) of lightproof, flexible material of a kind that will adhere to the surface to which it is placed, the retroreflectometer comprising: a source of light, consisting of a parabolic reflector (12) and a light bulb (14) mounted on a rod (9) free to move in the vertical plane and attached, at one end, to the spindle of a hinge (10) fixed internally to the base of the chamber (1) near the "window" (2) which bounds the sample (20) to be measured, and a convergent lens (16) also mounted on the rod (9) for the purpose of directing on to the sample (20) the beam or ray (17) of light emitted by the source (12, 14) so as to avoid dispersion, the rod (9) being inclinable in relation to the horizontal to at least 3 predetermined angles of inclination, suitable to be selected by means of a selector (18) that can be set from the outside; at least one photo-electric cell (24) able to receive the retroreflected beam or ray of light (25) from the sample (20) under examination, such photo-electric cell (24) being mounted on a small plate (23) fixed to a rotating axle (22) mounted transversely in respect with the side walls of the chamber (1), and in a position such that the length of the retroreflected ray striking the photo-electric cell is about half the focal length of the lens (16)--so that the photo-electric cell (24) is struck by a cone of retroreflected light sufficiently small to obviate the need for optical focusing and/or return systems--, said plate being capable of being set at at least three predetermined angles of inclination, by means of an external knob (26) which turns the axle (22); the value of degree of retroreflectivity of the sample measured by the photo-electric cell (24) being processed, stored and transduced PG,14 and so made available for reading on display (39).