The purpose of this study is to accomplish plane walking by a hydraulic-powered biped walking robot on a flat floor. Plane walking consists of three types of fundamental pattern walkings: straight walking, sideway walking and turning. The control method is a program control with a preset walking pattern. In forward walking the gait is a quasi-dynamic walking. We propose a new quasi-dynamic walking-control method as follows: change-over phase is divided into four phases according to the floor contact of soles, a walking pattern is designed by computer simulation and the output to a machine model is interpolated with a parabola function. In the other walkings the gaits are static walkings which are statically stable through all walking cycles. The model WL-10R is an anthropomorphic biped walking robot with 12 degrees of freedom driven by an electro-hydro servo mechanism. Additionally, WL-10R has a control device on its upper body. As a result of experiments, smooth and stable quasi-dynamic forward walking is achieved; the walking time is about 4.8s with 45cm stride. Stable static plane walkings are realized.