PURPOSE: To improve the efficiency of machining, by making the width of one of the two cutting sections of a gun drill larger than its radius and by making the width of the other smaller than the radius and by providing an oil passage groove across at the inner ends of both the cutting sections.

CONSTITUTION: A shank 2 provided with a V-shaped axial groove 3 on the peripheral surface is coupled to one end of a drive section 1 to be secured in a spindle. A very hard tip 4 is coupled to the front end of the shank 2. Cutting sections 5, 12 are provided on the front end of the tip 4 so that the cutting sections are opposed to each other in the diametral direction. The width of the cutting section 5 is larger than the radius of the drill but the width of the other cutting section 12 is smaller than the radius. An oil supply hole 10, which extends in the axial direction of the drill, is opened in the tip 4 to feed cutting oil to the cutting sections 5, 12. Chips are washed away by the cutting oil so that the chips are discharged to the outside through a groove 18 between the inner ends of the cutting sections 5, 12 and through another groove 16.