PURPOSE: To apply even for a coil spring of a dissimilar kind with a simple structure, by holding a locking claw freely movably in the diameter direction of a coil spring on a lockable holder at the vertical directional position driven in the axial direction of a dumper.

CONSTITUTION: A temporary assembly body S is held on a chuck device C, a coil spring 33 is compressed by a motor 6 and a locking claw 25 is advanced by an air cylinder 27. Even in case of the locking claw 25 being unable to infiltrate the interline of the coil spring 33, the coil spring 33 is compressed with further rotation of the motor 6, the locking claw 25 is infiltrated in the interline thereof and after the infiltration the locking claw 25 is descended as well according to the compression progress. The locking claw 25 is then pressed to the lower part by an air cylinder 26, a locking claw 29 is engaged with a lock bar 28 by the air cylinder of a lock mechanism R, a compression jig 8 is retreated to the upper part by reversing the motor 6 to set a spring receiver, the escape from a piston rod 31b is regulated by a nut and the locking claw 25 is retreated. The coil spring 33 is then extended and interposed in the compression state between the spring receiver and lower spring receiver 23.