A drill comprising a drill body which has a stick shape and is rotatable on an axis; wherein: chip evacuating flutes are formed in a periphery of the drill body from front flanks toward a rear side; cutting edges are formed along ridge lines where the front flanks and wall faces intersect with each other; the wall faces are in the chip evacuating flutes and face in a drill rotational direction; a cutting edge section in a front side of the drill body has an external diameter smaller toward the rear side in the axis direction than an external diameter at the cutting edges; a guide portion is provided to the rear side of the cutting edge section; the guide portion has a maximum external diameter part on the front periphery side thereof; an external diameter at the maximum external diameter part is larger than the external diameter at the rear of the cutting edge section, and is smaller than or equal to the external diameter at the cutting edges; the maximum external diameter part of the guide portion shows a smooth convex curve shape in a rotatory figure obtained by rotating the drill body on the axis; and a plurality of such guide portions are provided to the rear side of the cutting edge section, each of the guide portions having the same shape and size in the rotary figure, characterised in that the rear of each guide portion has an external diameter smaller than the external diameter at the maximum external part, and wherein from the rear of the cutting edge section to the maximum external diameter part of the next rearward guide portion, the shape is a convex arc with a radius, and the external diameter thereof increases radially outward in proportion to the rear direction, and wherein from the maximum external diameter part to a proximity point extremely close to it, the shape is still a convex arc with the radius, and the external diameter thereof slightly decreases radially inward in proportion to the rear direction, and from the proximity point toward the rear side, the shape is a straight line which is smoothly connected with the convex arc at the proximity point and goes toward the rear side, and the external diameter thereof decreases radially inward in proportion to the rear direction, wherein, in the rotary figure, from the rear of the guide portion to the maximum external diameter part of the next rearward guide portion, the shape is the smooth convex curve shape. chip evacuating flutes are formed in a periphery of the drill body from front flanks toward a rear side; cutting edges are formed along ridge lines where the front flanks and wall faces intersect with each other; the wall faces are in the chip evacuating flutes and face in a drill rotational direction; a cutting edge section in a front side of the drill body has an external diameter smaller toward the rear side in the axis direction than an external diameter at the cutting edges; a guide portion is provided to the rear side of the cutting edge section; the guide portion has a maximum external diameter part on the front periphery side thereof; an external diameter at the maximum external diameter part is larger than the external diameter at the rear of the cutting edge section, and is smaller than or equal to the external diameter at the cutting edges; the maximum external diameter part of the guide portion shows a smooth convex curve shape in a rotatory figure obtained by rotating the drill body on the axis; and a plurality of such guide portions are provided to the rear side of the cutting edge section, each of the guide portions having the same shape and size in the rotary figure, characterised in that the rear of each guide portion has an external diameter smaller than the external diameter at the maximum external part, and wherein from the rear of the cutting edge section to the maximum external diameter part of the next rearward guide portion, the shape is a convex arc with a radius, and the external diameter thereof increases radially outward in proportion to the rear direction, and wherein from the maximum external diameter part to a proximity point extremely close to it, the shape is still a convex arc with the radius, and the external diameter thereof slightly decreases radially inward in proportion to the rear direction, and from the proximity point toward the rear side, the shape is a straight line which is smoothly connected with the convex arc at the proximity point and goes toward the rear side, and the external diameter thereof decreases radially inward in proportion to the rear direction, wherein, in the rotary figure, from the rear of the guide portion to the maximum external diameter part of the next rearward guide portion, the shape is the smooth convex curve shape.