DRILLING DEVICE

PROBLEM TO BE SOLVED: To provide a drilling device capable of drilling with low torque and improving replacement operability for a drill bit.SOLUTION: A reverse gear device 9 can rotate a second drill bit 8 reversely to a rotating direction of a first bit drill 6, so the second drill bit 8 can cancel rotational reaction force generated by the first drill bit 6 to suppress the rotational reaction force. The reverse gear device 9 is installed in a cylindrical body 2, so the first drill bit 6 and second drill bit 8 can have sizes, shapes, etc., set without being restricted by the size of the reverse gear device 9. Consequently, the first drill bit 6 and second drill bit 8 are reducible in drilling resistance to drill with low torque. Further, the first drill bit 6 and second drill bit 8 having worn due to drilling can be replaced with new ones irrelevantly to the reverse gear device 9, so the first drill bit 6 and second drill bit 8 are improved in replacement operability.