Abstract: A length measuring apparatus for accurately measuring the length of a communication cable or other elongated object in the moving state and a method for the same. The preferable length measuring apparatus is a combination of a marking system and encoder system. The marking system counts the number of times a cable (1) moves by a standard length measurement distance (S) using that standard length measurement distance as one unit. To detect the conveyance of the cable by standard length measurement distances, a marker (43) makes marks (44) on the cable surface and the marks are detected by a laser switch or other sensor (46). The fine differences in distance between the standard length measurement distance and the mark interval (MS), that is, the surplus lengths (C.sub.1), are detected from the value of an encoder at the timing of detection of the marks.