This study aims at finding active biped robot designs with efficiency and simplicity of passive-dynamic walking. In this paper, it is shown that a biped robot with torso can walk efficiently on level ground over a wide range of speed by using torso and swing leg control based on passive-dynamic walking. A torso is used to generate active power replacing gravity, proposed by McGeer. The biped robot can exhibit a stable gait not planed in advance, and a period-doubling bifurcation is demonstrated in numerical simulations. Furthermore, when we choose carefully a swing leg control gain, a reverse period-doubling bifurcation from chaotic gaits to period-one gaits is demonstrated, which is not found in the passive-dynamic walking.