This paper deals with the development of the optical telemeter system, in which thetemperature of rotating spindle is measured with thermo-couple and the output is A/D converted and the digital data is transmitted from LED on the rotating head as optical data series. The size decreasing of the rotating head is achieved by three methods; the adoption of one-way data-transmission from the rotating head toward the stationary head, the adoption of one-chip micro-controller and the adoption of digital-filtering process in personal computer of stationary side. The measurement accuracy of the developed system is superior than 0.1--0.05℃ for 0--50℃ range. The data transmission rate is 6,200data/s of 12 bits data. And power for electric circuit in the rotating head is supplied by non-contact electro-magnetic phenomenon.