PURPOSE: To protect a running machine frame from damage, by removably coupling a crawler-adjusting female screw member to the running machine frame so that only the female screw member be deformed if abnormal load occurs.

CONSTITUTION: A female screw member 4 is removably attached by bolts 16 to a screw rod bearer 8 protruded from a running machine frame 5. An adjusting screw rod 3 is fixedly engaged in the female screw member 4 by a lock nut 9 so that the position of a rotary wheel 2 can be adjusted by rotating the adjusting screw rod 3. When an abnormal tension has occurred in a crawler 1, the rotary wheel 2 is pushed toward the screw rod 3 so that abnormal load is carried by the female screw member 4 through the screw rod. When the abnormal load has exceeded a prescribed level, the female screw member 4 is deformed or damaged so that the running machine frame is protected from damage.