There is currently research to support the construction of a walking assist machine, which machine uses a spatial parallel link mechanism for the elderly or rehabilitants. The flat steps of the assist machine move in parallel with the ground and can support the legs of a person including the soles. We developed a prototype and designed to assist people walking at up to fifty percent power. To grasp the walking phase of each leg of the equipped person, pressure sensors were laid under the thenar eminence and the heel of the sole, and the pressure variation at each sensing point was measured. For safety support, we developed a control method of the walking assist machine to fit the motion in phase by phase. Furthermore, in order to support walking indoors, we investigated the assist methods of turning around during walking and walking on a slope or stairs. A flexible link was installed in the mechanism for taking into account the twisting motions of the waist and ankle. To grasp the behavior of turning around during walking of the equipped person, pressure sensors were attached outside of the flexible link in both crural parts of the machine. As a result of the experiment wearing the machine, the equipped person could turn around during walking at will. To confirm the validity of the supporting method, muscle activity of the leg while wearing the walking assist machine evaluated by using the surface electromyography (called as "EMG"), and calculated the ratio of the integrated EMG (called as "IEMG") with and without the walking assist machine. The initial results show that the activities of the rectus femoris muscle and the tibialis anterior muscle can be held to approximately 60 percent by wearing the walking assist machine. Furthermore, in order to support walking indoors, we investigated the assist methods of walking on a slope or stairs. The machine was equipped with a gyro sensor and an ultrasonic sensor; the angle of the slope and the size of stairs could recognize and the machine could be controled according to the signals from the sensors. As a result of the experiment wearing the machine, the equipped person could walk on a slope or stairs at will. The subject assisted with the machine was able to walk on a slope up to the angle of plus or minus fifteen degrees.