A machining device (100) is adapted to be provided on a mount provided with a toolholder (2). The toolholder (2) is controllable to rotate and is adapted to be engaged with a tool (4). A primary coil (10) engaged with the tool holder (2) includes a first ferrite core (14) and a first coil assembly (16) detachably engaged with the first ferrite core (14). The first coil assembly (16) is modular molded, and is adhered to be an annular body having a first hollow portion (161). A piezoelectric actuator (20) is electrically connected to the pri mary coil (10) to drive the tool (4) to vi brate. The secondary coil (40) includes a second ferrite core (42) and a second coil assembly (44) detachably engaged with the second ferrite core (42). The second coil assembly (44) is modular molded to be an annular body having a second hollow portion (441).