PURPOSE: To lower a super large saw frame with good balance and to drastically reduce sliding resistance at a guide part by constituting so that a pressure of a predetermined size in the direction to lift the saw frame is applied to each of auxiliary cylinders on both sides of a main cylinder.

CONSTITUTION: Auxiliary cylinders 4 and 5 are provided on both sides of a main cylinder 3 between them, and a predetermined pressure in the direction to lift a saw frame 2 is applied to them. Due to this, when the saw frame 2 is lowered, back pressure is applied to its oil drain passage, respectively, the heavy saw frame 2 can be lowered with a good balance and its unbalanced load can be eliminated. As a result, sliding resistance between a guide column (a main column 6 and an auxiliary column 7) for guiding the saw frame 2 and a guide (main guide part 21 and an auxiliary guide part 22) can be reduced.