To shorten a sampling time of a sample.

A drill hole is continuously formed in the surface 8 to be sampled of a structure 6 through drilling in the direction of length and the direction of width along the outer periphery of a sample 7 about to be sampled. Thereafter, electric discharge machining is applied in the direction of the depth of the sample along a drill hole continued in the direction of the width of one side by a U-shaped electric discharge electrode 4. Consecutively, electric discharge machining is effected along drill holes on both sides continuous in the direction of length. Finally, electric discharge machining is effected in the direction of depth along a drill hole continuous in the direction of the width of other side. The sample 7 is then sampled. The drill hole is formed in such a manner that a guide jig having a through-hole continuously formed facing the drill hole is arranged on the surface 8 to be sampled and the drill is guided through the through-hole of the guide jig.