The optical device for determining position and orientation of an object comprising a fixed part comprises a laser beam projector with sequential scan and a projection centre (O), defining the centre of a reference frame (R) in space. The projector emits, in a zone comprising at least four sensors fixed to the said object, the four sensors having a known disposition on the object. The instants at which each of the sensors provides an electrical pulse determine the angular directions of the said sensors in the reference frame, the four straight lines passing through the origin and through each of the sensors intercepting an image plane of the fixed part at four projected points. The positions in the image plane of the mappings of the four points determine a geometric shape making it possible to calculate the position and the orientation of the object in space.