PURPOSE: To put the longer side of a carpenter's ruler on a pillar along the length direction of the pillar across a plate, etc., so that the slope angle of a roof beam, etc., can be easily and accurately set with the shorter side of the ruler by cutting off the outer intersecting corner section of the longer and shorter sides and forming a detouring outer intersection side having a desired shape and angle.

CONSTITUTION: A cut-off section 6 is formed at the outer intersecting corner 5 of the title carpenter's ruler 1 so that the longer side 3 of the ruler can be put on a pillar along the length direction of the pillar across a diaphragm, etc., installed on the pillar. Therefore, the shorter side 4 of the ruler l indicates the slope angle position of a roof beam or cross beam and, when the roof or cross beam is arranged along the side 4, the beam can be easily and accurately tack-welded at a prescribed gradient. In addition, a mark 8 or marks 8 indicating the slope angle of the ruler 1 are put on either one of the sides 3 and 4. The marks are numbers of, for example, '10' indicating a gradient 10/10, '4.5' indicating the gradient of tiled roofs of 4.5/10, '3' indicating the gradient of slate roofs of 3/10, '2' indicating the gradient of colored bestos roofs of 2/10 and, for example, a total of 10 kinds of numbers is prepared as one set.