A back posture straightening device includes an cable having two ends secured together to form an endless loop, and a bridge engaged between two segments of the cable for separating the segments of the cable from each other and for forming an eight (8)-shaped structure for the back posture straightening device and for engaging onto shoulder portions of a user, the bridge includes a base and an bar engaged with the segments of the cable, and the base and the bar are adjustable relative to each other for adjusting a distance between the segments of the cable.
