Packing bag and manufacturing method for the packing bag

A manufacturing method of packing bag to make a packing bag having a separation-prepared line portion, separable by predetermined tensile force by human hands, along an opening-prepared side portion, comprising the steps of:

• continuously running a sheet material of long resin having a layered unit construction in which first and second welding resin layers are disposed on both sides, and a barrier layer is disposed on a middle position;
• forming a half-cut first laser-worked groove concaved on the first welding resin layer of the running sheet material with measuring a first groove depth dimension of the first laser-worked groove and a half-cut second laser-worked groove concaved on the second welding resin layer with measuring a second groove depth dimension of the second laser-worked groove;
• and
• controlling a first laser beam forming the first laser-worked groove based on measuring results of the first groove depth dimension and a second laser beam forming the second laser-worked groove based on measuring results of the second groove depth dimension to form the separation-prepared line portion composed of the first and second laser-worked grooves barely damaging the barrier layer.