The utility model discloses a variable arc device, it includes support and variable arc subassembly, and variable arc subassembly includes variable arc mechanism and support mechanism, and variable arc mechanism includes a plurality of variable arc spare, and two variable arc spares of adjacent each other articulate, support mechanism includes first support spare and second support spare, and first support spare has first end and second end, and second support spare has third end and fourth end, first end articulates through first articulation axle with support, and second end articulates through second articulation axle with third end, and fourth end articulates through third articulation axle with variable arc spare, the axle line L1, L2, L3 of first articulation axle, second articulation axle, third articulation axle all are parallel with each other, the utility model sets up support mechanism, and first support spare and second support spare of support mechanism can only swing in the plane that is perpendicular to axle line L1, L2, L3 simultaneously, and support mechanism can provide support in the axial direction of axle line L1, L2, L3, and effectively maintain variable arc spare straightness and mechanism overall stability.