Packaging machine for packaging products in bags (101; 102; 103; 104), in particular loose products of small size or powder or granular products, comprising - a forming tube (2; 12) around which a film made of plastic material is wrapped that is unwound from a reel, - a feeding unit for dispensing into said forming tube (2; 12) defined doses of product to be packaged in said bags (101; 102; 103; 104); - a first welding unit for carrying out on said film at least a longitudinal weld (52; 53) parallel to a feed direction of said film along said forming tube (2; 12); - a second welding unit for carrying out on said film transverse welds (54; 55), in particular almost orthogonal to said feed direction, mounted rotatably about a rotation axis, in particular substantially parallel to said feed direction, so as to carry out transverse welds (54; 55) at least along two welding directions (B, C) that are orthogonal to each other and to said feed direction; and - moving means for supporting and moving said second welding unit along said feed direction with a reciprocating rectilinear motion, in particular said second welding unit carrying out said transversal welds (54; 55) in a working stroke while said film is moved with a continuous motion, said moving means comprising a carriage, supporting said second welding unit and slidingly connected to a supporting frame of said machine, and actuating means to move said carriage; said packaging machine being characterized in that said moving means further comprises balancing means arranged to cooperate with said actuating means for moving said carriage and comprising one or more cylinders in flowing connection with a reservoir of pressurised air, fixed to said supporting frame and connected with and acting on said carriage, wherein said balancing means comprises a couple of pneumatic cylinders fixed to said supporting frame and connected with and acting on said carriage, said pneumatic cylinders being in flowing connection with said reservoir that is provided with a valve adapted to make an established air-flow flow away from the reservoir into an outer environment, said reservoir being connected to and supplied by a source of pressurised air to restore the air leaking out through said valve, in particular to maintain a temperature of the air in said reservoir substantially constant. - a forming tube (2; 12) around which a film made of plastic material is wrapped that is unwound from a reel, - a feeding unit for dispensing into said forming tube (2; 12) defined doses of product to be packaged in said bags (101; 102; 103; 104); - a first welding unit for carrying out on said film at least a longitudinal weld (52; 53) parallel to a feed direction of said film along said forming tube (2; 12); - a second welding unit for carrying out on said film transverse welds (54; 55), in particular almost orthogonal to said feed direction, mounted rotatably about a rotation axis, in particular substantially parallel to said feed direction, so as to carry out transverse welds (54; 55) at least along two welding directions (B, C) that are orthogonal to each other and to said feed direction; and - moving means for supporting and moving said second welding unit along said feed direction with a reciprocating rectilinear motion, in particular said second welding unit carrying out said transversal welds (54; 55) in a working stroke while said film is moved with a continuous motion, said moving means comprising a carriage, supporting said second welding unit and slidingly connected to a supporting frame of said machine, and actuating means to move said carriage;