A drilling device, comprises: a supporting stand for holding a first drive device that rotates a first shaft about a first axis; a holder for holding a second drive device that rotates a second shaft about a second axis; and an offset mechanism coupled between the supporting stand and the holder, wherein the offset mechanism comprises: a controller movable between first and second positions (124, 126) to switch an outward displacement distance of the second axis with respect to the first axis between first and second distances; characterised in that the offset mechanism further comprises: a first adjusting element moveable with respect to the supporting stand, wherein the first adjusting element defines the first position and stops the controller from moving beyond the first position in a first direction away from the second position; and a second adjusting element moveable with respect to the supporting stand, wherein the second adjusting element defines the second position and stops the controller from moving beyond the second position in a second direction away from the first position, wherein the second adjusting element comprises a longitudinal through hole that allows the first adjusting element to pass therethrough. a supporting stand for holding a first drive device that rotates a first shaft about a first axis; a holder for holding a second drive device that rotates a second shaft about a second axis; and an offset mechanism coupled between the supporting stand and the holder, wherein the offset mechanism comprises: a controller movable between first and second positions (124, 126) to switch an outward displacement distance of the second axis with respect to the first axis between first and second distances; characterised in that the offset mechanism further comprises: a first adjusting element moveable with respect to the supporting stand, wherein the first adjusting element defines the first position and stops the controller from moving beyond the first position in a first direction away from the second position; and a second adjusting element moveable with respect to the supporting stand, wherein the second adjusting element defines the second position and stops the controller from moving beyond the second position in a second direction away from the first position, wherein the second adjusting element comprises a longitudinal through hole that allows the first adjusting element to pass therethrough. a controller movable between first and second positions (124, 126) to switch an outward displacement distance of the second axis with respect to the first axis between first and second distances; characterised in that the offset mechanism further comprises: a first adjusting element moveable with respect to the supporting stand, wherein the first adjusting element defines the first position and stops the controller from moving beyond the first position in a first direction away from the second position; and a second adjusting element moveable with respect to the supporting stand, wherein the second adjusting element defines the second position and stops the controller from moving beyond the second position in a second direction away from the first position, wherein the second adjusting element comprises a longitudinal through hole that allows the first adjusting element to pass therethrough. a first adjusting element moveable with respect to the supporting stand, wherein the first adjusting element defines the first position and stops the controller from moving beyond the first position in a first direction away from the second position; and a second adjusting element moveable with respect to the supporting stand, wherein the second adjusting element defines the second position and stops the controller from moving beyond the second position in a second direction away from the first position, wherein the second adjusting element comprises a longitudinal through hole that allows the first adjusting element to pass therethrough.