A packing machine includes a guide configured to guide a sheet of packaging material formed in a tubular shape, a sealing device configured to fuse an overlapping portion of the packaging material, a detection element pivotally attached to the guide and arranged downstream of the sealing device along a welded portion of the packaging material, a biasing member configured to bias the detection element outwardly from the guide, and a detector configured to detect the detection element that is pushed out from the welded portion.