PROBLEM TO BE SOLVED: To provide a drilling device that can accurately drilling a hole without requiring a time and effort for drilling operation, and to provide a method of the device.SOLUTION: The drilling device includes: a pressing leg 31 operable to press inner peripheral surfaces of fluid pipes 2, 4 in a radial direction, or to release the pressing, and supported to the fluid pipes 2, 4 while pressing the fluid pipes; a drilling unit 32 provided in the pressing leg 31 having a drilling blade 50 that can proceed and retreat in a radial direction and drilling the inner peripheral surfaces 3a, 5a of the fluid pipes 2, 4 to form drilled holes 3b, 5b; and a turning unit 33 for turning the drilling unit 32 by a predetermined rate in a circumferential direction of the fluid pipes 2, 4 relative to the pressing leg 31 in the pressing state and then fixing the drilling unit.