To prevent tail parts of strip metals from meandering and to surely execute a centering operation by pressing pats to strip metals from the upper and lower sides or either the upper side or the lower side with screw down devices before tail parts of strip metals leave payoff reels during threading.

Pats 7, 7a are arranged in the upper and lower sides of a pass line, and the pat 7a is pressed to the side of the pat 7 from the upper and lower sides or either the upper side or the lower side using screw down devices 8, 8a before tail parts of strip metals 3, 3a leave payoff reels 1, 1a during threading. A frictional force is generated between strip metals 3, 3a and pats 7, 7a by holding tail parts of strip metals 3, 3a with pats 7, 7a and giving a vertical stress to strip metals 3, 3a, whereby strip metals 3, 3a are restrained in the width direction. By this way, the meandering of strip metals 3, 3a is controlled.