PURPOSE: To obtain an instrument for measuring the roll attitude of rotary launched body, granade, etc., a missile and the like, with a polarized radio wave radiation wave.

CONSTITUTION: This Instrument consists of a transmitter 2 which is so provided as to send the polarized radiant space wave 4 for position measurement in the direction of a launched body 1 and a receiver 5 which is provided in the launched body 1 to receive the sent radiant wave 4. The sent space wave 4 meets carrier standards of a frequency f1 after phase modulation with a modulation frequency f2, where t2 is much less than f1 and a divisor of the carrier frequency f1.