Qualification tests of the ITER Toroidal Field (TF) conductor joints have been carried out by testing short joint samples with test facilities in National Institute for Fusion Science. The joint sample consists of two short TF conductors with the length of 1,535 mm, which is restricted by the conductor test facility with 9 T split coils and 100 kA current leads. Each conductor has two joint boxes at both ends. The lower joint is a testing part that is full size joint of the TF coil, where the cables is compacted from the void fraction of 33% to 25% on the length of 440 mm, the same as the final twisting pitch length. The total length of the joint box is 675 mm including the transition region of cable compaction. In order to attain the original conductor part of 300 mm length for setting voltage taps at three positions, the length of upper joint box is shortened to 560 mm, where the joint length of the cables and copper sleeve is shortened to 325 mm. The voltage drops between L-leg conductor and R-leg conductor are measured with six voltage taps per position per conductor while holding currents for three minutes at 1, 15, 30, 45, 60, 68 kA. The joint resistance of the lower joint is estimated from the increase of the average voltage drop among the six taps against the currents. Five joint samples were tested until 2016, and all the samples satisfied the requirement of the joint resistance less than 3 nano-ohms. The method of the measurement is explained and the voltage distribution among the voltage taps is discussed.