A lot of previous studies have developed various exercise methods and devices in order to provide exercise effective for maintaining good health. In particular, it is recently well-known that underwater gait-training is a useful fitness movement especially for elderly person. In addition, our previous study, it has been reported to develop a device to induce locomotor-like stepping movements by injecting jet-water to foot sole of a person sitting in a bath. And we demonstrated that the new device can induce locomotor-like stepping movement by effectively flexing hip, knee and ankle joints. In this study, we focused on optimization of this device. Here, we investigated relations of the cyclic (slow, fast) injecting jet-water and the locomotor-like stepping movement. The result shows that coefficient of variation (C.V.) of knee and hip joint was significantly larger in the slow cyclic injecting jet-water compared with that of fast cyclic. We suggested that different cyclic injecting jet-water modulate locomotor-like stepping movement.