PURPOSE: To dispense with the installation of a cable under the floor of a medical office and the installation of the cable on the floor by transmitting data with respect to dental treatment between a host computer which manages every kind of data for diagnosis and a microcomputer installed in a dental treatment instrument by using an optical communication means.

CONSTITUTION: Treatment data in the dental treatment instrument generated by the microcomputer 5 and X-ray image data obtained by an X-ray image processing computer are transmitted to and stored in the host computer 9 by using the optical communication means or radio communication means consisting of light emitting units 12, 15 and light receiving units 13, 16. While, past treatment data stored in the host computer 9, etc., is drawn in the microcomputer 5 similarly, and the data is displayed on a display 42. Therefore, the treatment posture of a dental treatment chair 7 and the optimum condition for medical instruments can be set when a doctor performs treatment, and also, the past treatment data of a patient can be referred.