To surely, efficiently, and safely cut a capacitor and a transformer.

A cutting device for cutting a closed box casing formed of a sheet metal comprises: a frame 3 on which a casing 101 is mounted for supporting a load; a clamp device 5 for moving the casing horizontally along the frame while holding the casing; a pair of cutting mechanisms 9 having respective cutting blades for cutting the casing and opposed to each other, gap guide devices 7 disposed on both sides of the frame liftably on to the casing cutting side relative to the cutting mechanisms and carrying a load on the casing, and a rotary table 4 disposed on the frame at any position and rotated about an axis in the vertical direction.