PURPOSE: To implement consistent capping to a container by rotating a thread roller around a pilfer-proof(PP) cap by a predetermined angle when the screw engagement start point of the thread roller is detected.

CONSTITUTION: When a container 1 having a pilfer-proof cap 5 previously fitted to its neck is positioned to a container grip mechanism 2, a controller 8 runs a torque motor 3 at a specified torque 11. The controller 8 monitors all the time real torques 12 to 14 of a capping head 4 for a value larger than a predetermined torque to detect an engagement start point 1c in which a thread roller 4b begins to engage a root 1b of a screw 1a. With the detection of the engagement start point, the controller 8 finds an rotation angle of the capping head 4 from an output signal of a rotation detector 6, and terminates the capping when the thread roller 4b turns by a previously specified angle from the engagement start point 1c.