PURPOSE: To transmit one-to-one turning torque even in a remarkably bent form by providing a transmitter formed by three springs different in inside and outside diameters and spirally wound co-axially with one another, and arranging the springs to form an interference fit between the center spring and a set of the inner and outer springs.

CONSTITUTION: A transmitter 10 is formed by three spirally wrapped wire springs 12, 14, 16. These are co-axial, the respective springs are wrapped at a spiral angle of about 7 degrees with a side edge of mutual adjacent wire turns, the springs 12 and 16 are wrapped right-handed and the spring 14 is wrapped left-handed. The ends of the three springs are mutually brazed or soldered, and the remaining parts of the springs are engaged to be relatively moved. When the springs are relaxed not to come into contact with each other the inside diameter of the spring 14 is smaller than the outside diameter of the spring 12, and the outside diameter of one spring 14 is larger than the inside diameter of the spring 16. That is, an interference fit is existent among the springs 14, 12, 16.