To improve a function of an apparatus for punching a hole with an undercut part to cut the undercut part at an inner most part of the hole simultaneously by punching a drill hole.

A base 6 having an intermediate contracted part 6a is fixed to a main body 1 to be punched. A cylindrical sleeve 7 is arranged on the base. A lifting spring 9 is interposed between a lower part of the sleeve and an upper end of an undercut part cutting member 5 attached to a side of a drill cutter 4 of the main body. A press moving plate 10 brought into slidable contact at a plurality of positions with an inner surface of the sleeve is coupled to an upper end of the undercut part cutting member. A lower end of a first shock transmitting rod 13 locked at an upper end to one locking step 12a of a cam 12 shaft mounted at a groove-like space of the base is brought into contact with a lower part of the sleeve 7. And, a lower end of a second shock transmitting rod 14 locked to the other locking step 12a of the cam 12 is brought into contact with the plate 10.