PURPOSE: To obtain an apparatus for determining the roll angle position of a rotating projectile, a bullet, a missile or the like by polarized electromagnetic radiation. CONSTITUTION: An apparatus for determining the roll angle position comprises transmitters 2 and 4 for emtting position determining polarized radiation in the direction toward a projectile 1 and receivers 7 and 9 arranged in the projectile for receiving the transmitted radiation. The emitted radiation consists of two components, a component in the long-wave band and a component in the microwave band. The microwave component comprises a pulse train in which the pulses indicate a time when the long-wave component is situated in a certain pulse position. Specifically, the pulses indicate the sinusoidal long-wave component's zero cross-overs with a positive derivative. This is generated in such a way that a synchronizing pulse is emitted by the long-wave transmitter 2 to the microwave transmitter 4 which transmits a short series of microwave pulses as an indication to the projectile 1.