A volume measuring apparatus having a first camera, a second camera, an emitting unit and a processing unit is disclosed. The processing unit controls the emitting unit to emit invisible structure light, and controls the first and second camera to capture a left and a right image both containing a target-box. The processing unit generates a depth graph according to the left and right image, and scans the depth graph through multiple scanning lines for determining a middle line, a bottom line, a left-sideline, and a right-sideline of the target-box in the depth graph. The processing unit performs scanning, within a range of the middle line, the bottom line, the left-sideline, and the right-sideline, for obtaining a plurality of width information, height information, and length information. The processing unit computes the volume related data of the target-box according to the plurality of width information, height information, and length information.