PURPOSE: To provide a drilling method for a piled soft and hard materials with a gun drill capable of accurately drilling.

CONSTITUTION: In piled hole drilling of assembly constituting parts with a gun drill 3 which is performed in order from acryl material 7 of a bad electric conductor to aluminum material 9 of good conductor, voltage is applied between the acryl material 7 and the aluminum material 9, after detecting contact between the gun drill 3 and the aluminum material 9, and during a specified time hereafter, cutting feed of the gun drill 3 is automatically stopped, and as for the incomplete drilling part position of the aluminum material 9, pilot drilling with a hand bush 12 and a twist drill 13 and then correct dimensional drilling with a stepped twist drill 14 are executed.