To provide a drilling machine for a brittle material for a drill to be detachably fixed to a drill rod surely by a lock coupling part and capable of a transmitting a drilling torque.

For the purpose of relatively accurate positioning, a drill head (2) has a conical shape part (10), which is engaged at its center within a corresponding receiving port (11) of the drill rod (3) in an operating state as shown. As an axial looseness preventing means, a restricting member (15) constituted as a hollow nut is provided to be engaged with threads (16) of the head having a reverse pitch and threads (17) of the rod. The head and the rod can be simply clamped to each other or separated from each other by rotating the member. The coupling part enclosed by the member is simultaneously optimally protected against an external influence. Accordingly, a drilling machine (1) can accurately drill without excess wear or complicate handling.