A box-opening device is disclosed. The box-opening device includes a first holding part that holds a first surface and a second holding part that holds a second surface. The first surface is one of two adjacent surfaces of a folded corrugated cardboard sheet, and the second surface is the other of the two adjacent surfaces of the corrugated cardboard sheet. The box-opening device also includes a first holding part movement mechanism which changes a position of the first holding part with respect to the second holding part and thereby transforms the corrugated cardboard sheet into an opened state. The first holding part movement mechanism has a support member that supports the first holding part so that the part rotates on an arc track about a central axis of rotation that overlaps an imaginary line extending along a boundary line between the first surface and the second surface.