A band saw machine with a rod having an adjustable position to accommodate various sized workpieces includes a movable member which is mounted on a saw frame and movable relative to a movable clamp arm. The movable member and the fixing member each have a rack, and the racks are in parallel to each other. The rod includes a gear shaft engaged with the racks. When the movable clamp arm moves to accommodate the size of a workpiece, the rack of the movable member drives the gear shaft to move along the rack of the fixing member, which causes position change of the rod, so that the rod is automatically moved to a position where it can detect the workpiece in a reliable manner. Therefore, the size of the workpiece to be clamped is not limited by the position of the rod anymore.