Biped robots require a high power to be provided alternately on their two legs while walking, hopping, and running. However, the mounting of high-power and large electrical motors is challenging in conventional mechanical transmission systems because of space limitations. To address this issue, we employ herein a combination of hydraulic and transmission systems with an independent driving mode and a power-shared driving mode. In the independent driving mode, an actuator can be independently controlled based on flow-control, and pressure loss can be reduced. In the power-shared driving mode, actuators can also be controlled based on flow-control, and this mode allows the motor power of the left and right legs to be shared. We also employ a simulation to evaluate the proposed novel system and confirm that the motor power could be reduced by 35.6% for the hopping movement. This result shows that the rated output of the required motor can be reduced, and the selection of smaller and lighter motors is possible for installation in biped robots.