To protect a travel device or the like by absorbing and alleviating excessive tension appearing on a crawler during the travel of a construction machine or the like.

The rod 5 of an adjuster cylinder 4 for adjusting the tension of a crawler, and a greasing block 6 are provided with a check plate 11 having a built-in discharge check valve 12a and greasing check valve 12b to open at internal pressure equal to or above the set pressure of the adjuster cylinder 4. Furthermore, a reserve cylinder 8 is mounted on the check plate 11. This reserve cylinder 8 is internally partitioned into a large diameter side oil chamber 21 and a small diameter side grease chamber 22 by means of a freely slidable piston 13. Also, a selector valve 7 fitted to the side of the reserve cylinder 8 is internally provided with a spool 10 operable on a balance between hydraulic pressure taken out from the large diameter side oil chamber 21 of the reserve cylinder 8 and own travel hydraulic pressure. The spool 10 controls the travel hydraulic pressure for the feed thereof to the large diameter side chamber 21.