Many kinds of burrs are formed in various fabricating processes. These burrs are often manually removed even in modern factories. Therefore, these burrs make troubles on production lines in terms of automation, quality of products and working environment. In this paper, the burr formation mechanism on the exit side in drilling of metals is discussed. The idea is that the burr formation mechanism is equivalent to that of the deflection of cantilever changing the thickness under equiload. On the basis of the idea, authors have designed the burrless drill, in which the corner of cutting edge is cut by a little larger compared with a normal drill. The effect of the burrless drill is discussed in the present paper.