The speed of development of biped robots has been slow despite of much interest and investment for research since 1960's. One of main reasons is that the actuators with the speed reducer had weakness in supporting the weight of the body and leg itself. To overcome this, a new four bar link mechanism actuated by the ball screw is proposed. The four bar mechanism has higher strength and gear ratio than conventional actuators to actuate the leg of the biped robot. Using this, new autonomous type of 10 degree-of-freedom biped robot is developed to perform autonomously such that it is actuated by small torque motors and boarded with a DC battery and controllers. One leg was designed to have ankle, thigh, and hip joints. Each leg of the robot composes of three pitch joints and one roll joint. The dynamics model of the biped robot is investigated. In the modeling process, the robot dynamics are expressed in the joint coordinates using the Euler-Lagrange equation. Then, they are converted into the sliding joint coordinates, and joint torques are expressed in the forces along the sliding direction of the ball screw. To validate the model of the robot, a computer simulation is performed and the developed biped robot performs motions of sitting-up and down. Through a series of the experiments, the capability of biped-walking can be found.