Résumé dans la langue de publication, traduction non disponible In directing incident light Li from a projecting unit 6 to the surface 1a of the paper 1 to be measured at a given angle (theta i) of incidence and receiving by a receiving unit 7 the intensity of light reflected Lo by and off the surface 1a of the paper 1 at the same angle (theta o) of regular reflection as the angle (theta i) of incidence, the incident light Li containing at least the linearly polarized principal ray is allowed to be incident on the surface 1a of the paper 1, so that at least the linearly polarized principal ray can be received by the receiving unit 7 in the form of reflected light Lo, and the surface 1a of the paper 1 is inclined at an angle (alpha ) of inclination around the line of intersection of a plane M of incidence and reflection through which the incident light Li and reflected light Lo pass with the surface 1a of the paper 1 while the paper 1 is rotated relative to the plane of incidence and reflection around the center axis of rotation defined by a line that passes through a center point 3 of the surface 1a of the paper 1 irradiated with the incident light and is vertical to the surface of the paper, whereby the fiber orientation on the surface 1a of the paper 1 can be found from the intensity of the reflected light Lo received by the receiving unit 7 corresponding to the angle of rotation of the paper 1.