PURPOSE: To perform formation of a bent hole through a simple mechanism and to perform sufficient excellent formation of a small bent hole.

CONSTITUTION: A bent hole machining device comprises an electrode tool 8 for machining; a flexible tool support member 7 to support an electrode tool 8 for machining; and an insulating material 11 to expose the surface, except a given part in the progressing direction of machining, of the surface of the electrode tool 8 for machining and keep an angle of the progressing direction of the electrode tool 8 for machining with an exposure direction at a constant value or change the angle. Further, the bent hole machining device comprises a dielectric 12 to energize the electrode tool 18 for machining; a machining liquid feed flow passage 14 through which machining liquid 13 is fed to a machining part; and a machining chip discharge flow passage 16 through which machining chips 15 are discharged togetherwith machining liquid from the machining part.