To provide an internally cooling type drilling tool that improves a flow rate of cooling water as well as durability to breakage, pressure, twisting, and bending.

An inner cooling channel 3 is formed on each web 2 of the drilling tool. The cooling channel extends from the tip of the tool to an opposite drill end and has a continuously extending cross-sectional contour 30 enclosing an imaginary circle K with a center point M. The cross-sectional contour 30 of the inner cooling channel 3 preferably comprises two maximum curvature values whose distance to the drill axis A is greater in the direction of a line between the center point M and the drill axis A or equal to the distance of the center point M to the drill axis A. The minimum wall thicknesses exist between the inner cooling channel 3 and the outer periphery of the drill 7, between the inner cooling channel 3 and the machined surface 5 and between the inner cooling channel 3 and the non-machined surface 6, ranging from a minimum threshold to a maximum threshold. The lower and upper thresholds, along with the geometry of the internal cooling channel, are optimized in relation to the through-flow of coolant and to the stability of the tool.