PURPOSE:To safely measure the draft line without being influenced by waves by inserting a scale wire having a float at the top edge in a telescope type guide type suspended from a broadside and driving-in/out a guide pipe according to the scale wire driving-in/out quantity. CONSTITUTION:A piece of the supporting metalware 2 is rotatably connected with a hinge 2 installed on a hull 1, and a telescope type guide pipe 4 is connected and suspended through a hinge 2a. A scale wire 5 is inserted through the inside of the pipe 4, and a float 7 is installed at the top edge of the wire 5, and the wire 5 is driven-in/out by a winch 8. When the pipe 4 is suspended from a broadside, and the wire 5 is driven out by the winch, the float 7 is separated from a stopper 10, and driven out downward, and then also the guide pipe 4 is lowered and extended, and the lower edge is immersed under the draft line 6. Accordingly, the float 7 is floated up on the draft line 6, and the draft is measured by the scale on the wire 5 without being influenced by waves.