A digital image-capturing device includes an outer lens barrel, an image sensor disposed in the outer lens barrel, an inner lens barrel mounted in the outer lens barrel, and a lens module mounted in the inner lens barrel. The outer lens barrel has a barrel coupling segment formed with an internal screw thread, and a barrel guiding segment. The inner lens barrel has a barrel engaging segment formed with an external screw thread to engage threadedly the internal screw thread of the barrel coupling segment, and a barrel sliding segment in sliding and rotatable contact with the barrel guiding segment. When the inner lens barrel is inserted into the outer lens barrel, the barrel guiding segment can guide the barrel sliding segment to prevent the inner lens barrel from wobbling and to maintain optical axis alignment, thereby ensuring image-capturing quality of the device.