The dependence of the ion temperature on various parameters (line-averaged electron density e, plasma current Ip and toroidal magnetic field Bt) was investigated for the JAERI-tokamak devices JFT-2 and JFT-2a with a 10-channel neutral particle energy analyzer. The measurements were performed by keeping two of the three parameters nearly constant, and they showed that the ion temperature obey the one-third power law in e, Ip and Bt. The ranges of the parameters were 0.7×1013e1.8×1013 cm-3, 14Ip170 kA and 10Bt18 kG. The measured ion temperature ranged from 80 to 350 eV and was (½-¼) of the central electron temperature. It followed the scaling law by Artsimovich Ti=Km(IpBteR2)1/3 with the numerical constant Km=(4.3-6.7)×10-7 in eV (AGcm-3cm2)-1/3.