PURPOSE: To measure the turning angle in a space when a human body and the like are in the moving state, by using a light, compact inertialbody supporting type measuring instrument, using a dynamic-torque balancing method in measurement, processing the output by using a computer using ICs, and computing the turning angle.

CONSTITUTION: A pair of inertial cut wheels 13a and 13b, whose weights are balanced, are attached to one end of a pointer 2, which is connected to a movable coil 1. Inertial moment in a movable part (u) is increased. With the inertial torque when a moving body is turned as input torque, the torque is imparted to the movable part (u) including a the movable coil 1. The displacement of the other tip of the pointer 2 from the zero position is detected by a detecting part (d). The displacement is converted into an electric signal. The signal is amplified by a amplifier part (a) and outputted to an output terminal 8. The output of the output terminal 8 is negatively fed back to the coil 1 through a feedback circuit (f). The output at the output terminal 8, which is obtained by applying the difference between the input torque and the torque caused by the feedback current to the coil 1, is integrated twice by a computer, and the turning angle of the moving body in the space during the movement can be obtained.