Abstract: The invention concerns apparatus for detecting the position of incidence (2) of a beam (1) of charge carriers on a target (3) wherein X-rays (4) starting from the position of incidence (2) are detected by detector (7) connected to an analyzing circuit (9) An imaging system (5, 50; 10, 11, 12) is provided which can cover all the positions (P.sub.1 . . . P.sub.8) that the positions of incidence (2) can take up and projects them on the sensing surface of a position-sensitive detector (7), wherein the projected coordinates (x', y') are directly proportional to the coordinates (x, y) of the position of incidence (2). In addition, a filter (6) highly transparent to the X-ray radiation range emitted from the position of incidence (2) is arranged between the target surface (3) and the position-sensitive sensor (7). The position-sensitive detector (7) emits electric signals which depend from the coordinates (x, y) of the position of incidence (FIG. 1).