To greatly save the number of workers and working time by forming a ridge forming the angle at the tip part of a tool to a cutting edge having an acute angle in the cross section.

Both end parts of a U-shaped material 1 parallel arranged is integrately welded with a connecting material 2 to form a guide frame 3, and the U-shaped material is used to a slide base 4 and in this material, an air hammer 6 is fitted through a bracket 5. The slide base 4 is fixed to a desirable position on the guide frame 3 with a set screw, etc. A boring tool 24a is fitted to a tool head at the lower end of the air hammer 6. The boring tool 24a provides a sharp polygonal cross sectional tip part having plural angles and the ridge forming the angle at the tip part is formed as the cutting edge 25 having the acute angle in the cross section. By this constitution, a hole for rainwater arranged at an eave of a metallic roof plate can be bored with momentary movement.