A chip discharge flute 22 is formed on the side surface of a drill main body 21 to be rotated about an axial line from the tip to the base end of the drill main body 21 and a cutting edge 25 is formed along the intersecting ridge where the wall surface 23 of the chip discharge flute 22 facing to the drill rotational direction thereof intersects with the tip flank 24 of the main body 21. A first cutting edge 26 is formed to a core thick portion at the tip of the drill main body 21 and linearly extending substantially from a rotational from a rotation center C of the drill by being applied with thinning, Further, three thinning surfaces 30, 31 and 32 are formed by the thinning at the intersecting portion where a wall surface 27 facing to the rear side of the drill rotational direction of the chip discharge flute 22 intersects with the tip flank 24, wherein the first thinning surface 30 faces to the drill rotational direction and is disposed to substantially stretch to the rotation center C of drill to define the first cutting edge along the intersecting ridge intersecting with the tip flank, the second thinning surface 31 faces to the external circumference of the drill main body 21, substantially stretches to the rotation center C of the drill and is disposed to intersect with the first thinning surface 30 by being curved to a concave shape, and the third thinning surface 32 faces to the rear side of the drill rotational direction and is disposed to the heel 28 side of the second thinning surface 31 so as to be curved to a concave shape with respect to the second thinning surface 31.