PURPOSE: To facilitate installing and removing work for a guide trough of a rolling mill by attaching a cover assembly so that a roll stand is adjustably moved to an open position so as to allow access to work rolls or to a guide position where a trough is aligned witch a rolling line.

CONSTITUTION: When existing in a closed position, a cover assembly 20 is placed on a parallel support flange 28 forming a part of a roll stand 10. The cover assembly 20 in the closed position cooperates with the lower side roll stand 10 to confine work rolls in the enclosing space 30, and workers are protected from a cobble related accident. Also, when access to the work rolls is necessitated, the cover assembly 20 is rocked upward up to a complete open position by exciting a rotational actuator 22. And a guide trough 24 is integrally incorporated into the cover assembly 20 rotationally adjustable to the rolling line, and whereby the guide trough is easily arranged.