PURPOSE: To provide a spring tensing device adapted to especially tense a coil spring of a buffer stud usable regardless of the size of a coil spring and the tensing force and easily operated with small force.

CONSTITUTION: A coil connecting part constructed as a coil spindle 4 for mutually controling the space between two spring holders is rotatable in a connecting member constructed as a base plate 3 on one hand and a cover plate 5 on the other hand between two guide rods 7, 8, and slidable spring holders 1a, 1b, 2a, 2b include a guide plate 6 guided to slide by a guide rod. The guide plate has a female screw thread 6a for receiving the coil spindle 4 between two guide surfaces 6b, a spring holder loosely encloses the outer periphery of the coil spring 10 tensed therebetween at least in a 180-degree arc, and at least one spring holder is arranged to agree with the spring pitch 10b.