Abstract: A strap reserving control device for a strapping machine is to apply the relative action between a balancing weight unit and a balancing rod respectively fixed at the opposite ends of a rotating shaft, and the functions of sensing by a sensing portion of a sensing switch to control the amount of packaging strap stored in a strap reserving room. The balancing weight unit and the balancing rod is formed with a lever structure therebetween, therefore no tiredness of elasticity or damage may happen to them, able to prolong the service life of the machine, and stably and precisely control the amount of packaging strap stored in the strap reserving room.