The purpose of this study is to provide a new approach for detection using bio-impedance. This impedance is measured by the four-electrode method. As the impedance changes resulting from ankle, knee, and hip movements depended heavily on electrode placement, we determined the optimal electrode configurations for those movements by searching for high correlation coefficients, large impedance changes, and minimum interferences in ten subjects (Age: 204). Our optimal electrode configurations showed very strong relationships between the ankle joint angle and ankle impedance (γ = -0.9130.03), between the knee joint angle and knee impedance (γ = 0.9440.02), and between the hip joint angle and hip impedance (γ = 0.8230.08). This study showed the possibility that lower leg movement could be easily measured by impedance measurement system with two pairs of skin-electrodes.