A device for measuring the retroreflective coefficient of an object comprising: an imaging unit being a camera for capturing an image (51, 52) of a target object, the imaging unit comprising a lens; a light emitting unit that is the light source for emitting light to illuminate the object with an incident light illuminance I; an observation angle acquiring unit for acquiring an observation angle (cp) determined by a positional relationship between the imaging unit, the light source for emitting light and the target object, wherein the observation angle is calculated as arctan (d/r), wherein d is the distance between the imaging unit and the light emitting unit and wherein r is the distance from the lens of the imaging unit to the target object derived using auto focus information from the imaging unit; an entrance angle acquiring unit for acquiring an entrance angle (θ) of light incident on the target object, based on incline angle information from a detecting unit, wherein the entrance angle is an angle between the normal direction of the target object and the incident direction from which light incidents on the target object; a converting unit (141, 141A, 141C) for converting image data of an image to a luminance value L of the target object using capture information of the image, such as effective aperture value, shutter speed, ISO sensitivity, focal length, capture distance; and a calculating unit for calculating a value of a retroreflective coefficient RA(cd/ m 2 lx) of the target object based on an illuminance value I and the luminance value L of the target object, wherein the retroreflective coefficient is defined by the ratio of a retroreflective luminance L(cd/m 2) relative to an incident light illuminance I(lx). an imaging unit being a camera for capturing an image (51, 52) of a target object, the imaging unit comprising a lens; a light emitting unit that is the light source for emitting light to illuminate the object with an incident light illuminance I; an observation angle acquiring unit for acquiring an observation angle (cp) determined by a positional relationship between the imaging unit, the light source for emitting light and the target object, wherein the observation angle is calculated as arctan (d/r), wherein d is the distance between the imaging unit and the light emitting unit and wherein r is the distance from the lens of the imaging unit to the target object derived using auto focus information from the imaging unit; an entrance angle acquiring unit for acquiring an entrance angle (θ) of light incident on the target object, based on incline angle information from a detecting unit, wherein the entrance angle is an angle between the normal direction of the target object and the incident direction from which light incidents on the target object; a converting unit (141, 141A, 141C) for converting image data of an image to a luminance value L of the target object using capture information of the image, such as effective aperture value, shutter speed, ISO sensitivity, focal length, capture distance; and a calculating unit for calculating a value of a retroreflective coefficient RA(cd/ m 2 lx) of the target object based on an illuminance value I and the luminance value L of the target object, wherein the retroreflective coefficient is defined by the ratio of a retroreflective luminance L(cd/m 2) relative to an incident light illuminance I(lx).