PURPOSE: To improve the precision and the reliability of data by transmitting data from a rotary member through the use of optical fiber technique so as to remove electromagnetic interference.

CONSTITUTION: An analog sensor 4 is arranged inside the rotary member 2. The sensor 4 plurally includes straingages, thermo-couples and the other sensors, which detect the state of the rotary member and provides an analog electrical signal equivalent to it, and is connected to a data acquisition circuit 6 arranged inside the rotary member 2. The sensor device 4, the data acquisition conversion circuit 6, a logic circuit 32 and LED 8 rotate with the rotary member 2. An optical fiber bundle 14 reaches a decoder 16 from a light emitting device 20 through a housing 12. The decoder 16 converts the transmitted optical signal to an electrical digital signal. This signal is impressed to a processor or a computer 18 to properly signal-processed and sent to a utilizing device like a display and/or a recorder 22.