To clearly and accurately display a cutting plane line regardless of a position of a saw blade, by comprising a revolving arm projecting over a base in a feeding direction or a cutting direction, and supporting a cutting plane line display by an free edge part of the revolving arm.

When a cutting plane line display 11 is used, the cutting plane line display 11 is matched on a flat surface of a saw blade 4, and is guided along a marking line 27, and then a hand circular saw machine 6 makes the cutting forward motion. When the cutting plane line display 11 is not used, a revolving arm 10 can be revolved on an axis X-X so that it is located on a protective hood with the cutting plane line display. Accordingly the hand circular saw machine 6 is not enlarged by the revolving arm 10, and the revolving arm 10 is not bulky, and is not located on a position where it is exposed to the danger of damage.