telescopic ladder element 4 are also constructed with a preferably square hollow profile and are compressed such at their ends that the ends can be guided into the longitudinal groove 9 the crosspieces 8 are fastened to the sidepiece 7 by means of a welding seam 20 an opening 7a exists on the side surface of the sidepiece 7 into which opening is guided a guide sleeve 21 in which is supported a locking knob 10 or rather its bolt 11 the guide sleeve 21 has an enlarged head part 21a at one end thereof as well as a groove 22 therein axially spaced from the enlarged head 21a about the thickness of the wall of the sidepieces 7 as is particularly shown in fig4 in which is arranged a locking element 12 preferably in the form of a wire shaped spring element two annular grooves 23 24 are provided on the outer periphery of the bolt 11 with the annular groove 24 being thereby provided adjacent an end area of the bolt 11 remote from the looking knob 10 while the annular groove 23 is constructed at the area adjacent the locking knob 10 the annular grooves 23 24 are designed such that the spring like locking element 12 can be moved into the annular groove 23 or 24 to engage the locking knob 10 it is thus possible to lock the locking knob 10 in the position shown in fig4 in which it projects into the recess of the crosspiece 3 and assures a safe fixation of the telescopic ladder element 4 relative to the ladder.