An automatic reel unwinding apparatus in a machine for packaging products having a bearer structure (14, 15) carrying a pair of rotating arms (16), centrally hinged to the bearer structure (15) through a rotation shaft (17) and carrying at their ends, on two shafts (18, 18′), at least a pair of reels (12, 12′), the rotation shaft (17) being commanded through a speed reducer (20) and each of the two shafts (18, 18′) being commanded by a motor reducer (21) through a respective transmission (22) able to be selectively engaged with the motor reducer, the withdrawable shafts (18, 18′) being fixed to at least one openable support (19, 19′) arranged at an end of the arms (16).