PURPOSE: To measure the torque of a rotating body accurately without exerting any adverse influence upon a rotating body with simple structure.

CONSTITUTION: When a rotor shaft 10B is rotated by supplying a specific current to a motor 10A to be measured, a frictional force is generated between the shaft 10B and a thread 20 to apply tensile forces F1 and F2 to both ends of the thread 20. When the thread 20 is applied with the tensile forces F1 and F2, strain gauges 40A and 40B detect the tensile forces respectively and output detection signals V1 and V2 of strain to an adder subtracter 50A. The adder subtracter 50A calculates the difference between the detection signals V1 and V2 and outputs a signal, so a multiplier 50B multiplies the signal by a proportional coefficient R' and a constant K and outputs the resulting load torque signal Vt to a measuring circuit. This detection signal Vt is supplied to the motor 10A to be measured to obtain an electric signal proportional to load torque T0.