PURPOSE: To easily and quickly adjust the position of a table on a base by releasing or restraining the table from/to the base through only rotating a cam rod in a normal or reverse direction by operating a handle.

CONSTITUTION: In adjusting the position of a table 2 on a base, a handle is operated to rotate a cam rod 170 in another direction. This causes the cam rod 170 to release a fixing bolt operation piece 174, and it to release a fixing bolt 177. Consequently the table 2 is released from the base to become movable on the base. In fixing the table 2 onto the base, the handle is reversely operated to rotate the cam rod 170 in a reverse direction. This causes the cam rod 170 to restrain the fixing bolt operation piece 174, and it to restrain the fixing bolt 177.