PURPOSE: To directly read the torsional resistance of a power transmission shaft system with an indicator by providing each gear train in a drive side provided in one end of a coil spring and a driven side provided in the other end, and detecting torsion angle of the coil spring.

CONSTITUTION: One end of a coil spring 1 is fixed to a drive side block 2, and a driven side block 3 is fixed to the other end. At this stage, in the case where a truck 5 is fixed, the rotation of a driving source 4 is transmitted to the drive side block 2, and a bevel gear 11 is rotated at the same time. The rotation of the bevel gear 11 is transmitted to a bevel gear 12 and a shaft 13, and the rotation of the drive side block 2 is transmitted to the driven side block 3 through the spring 1. The rotation of the driven side block 3 is transmitted to spur gears 17, 18, bevel gears 20, 22, a sleeve 24, bevel gears 23, 25, 14 through an outer cylinder 10. Quantity of the torsional resistance given to the spring 1 through the driven side block 3 due to the resistance of the driven side is detected as the quantity of torsion angle on the basis of the angle of rotation of the bevel gear 14 through a differential bevel gear device.