1. A disparity calculating method for a stereo-matching device, used for calculating a plurality of disparities between a plurality of pixels of a first image-block and of a second image-block in a current frame, the disparity calculating method comprising: generating an energy matrix according to the first image-block and the second image-block, wherein the energy matrix comprises a plurality of energies of a plurality of pixels corresponding to a plurality of disparity candidates; setting the energy corresponding to a starting pixel of the plurality of pixels and a specified disparity candidate of the plurality of disparity candidates as a first predetermined value and setting the energies corresponding to the starting pixel and remaining disparity candidates of the plurality of disparity candidates as a second predetermined value, wherein the second predetermined value is greater than the first predetermined value; generating a path matrix according to the energy matrix; and determining the plurality of disparities of the plurality of pixels sequentially from an ending pixel of the plurality of pixels, wherein the disparity of the ending pixel is set as a third predetermined value.