The shoulder strap is hidden, and when the zipper is pulled up, it instantly transforms into a trolley and can be used as a trolley bag. It adopts silent wheels, shock absorption and noise reduction, and stable bearings for strong support. Ultra-quiet, smooth and smooth, durable, easy to climb stairs, and reduce resistance and vibration when pulling the backpack. Double reinforcement prevents the chassis from being hit and worn by hard objects splashed by dragging. Two-speed adjustable tie rods and one pair of tie rods, 3000 times of continuous pulling and closing are as smooth as ever. Considering the safety of the backpack's personal items, the backpack is equipped with an anti-theft plus password lock embedded in the sunken embedded design, which is fully upgraded. Hidden strap + hidden trolley, can be pulled back, powerful storage function, making your travel easier.