A height measuring device, including a scale, including graduation and a measuring part, and a positioning plate, the graduation and the measuring part are disposed on a right side of the scale, the measuring part is capable of moving along the graduation and indicating height, a measuring plate is disposed on the measuring part, and capable of folding as being perpendicular to or parallel to the scale, a top edge of the scale is capable of being buckled with a bottom edge of the positioning plate, a bottom edge of the scale is capable of being buckled with a top edge of the positioning plate, and a fixing part is disposed at the back of each of the scale and the positioning plate, and capable of being disposed in a vertical plane.