An inexpensive charging system with a simple construction is capable of supplying charging current to a battery of a legged walking robot while maintaining the supply of required current to an electric load of the legged walking robot by an external power source. The charging system includes a connection circuit having a first diode that brings the positive electrode of the battery and the positive input terminal of the electric load into conduction, defining the direction from the positive electrode of the battery to the electric load as a forward direction, a second diode that brings the positive electrode of the external power source and the positive input terminal of the electric load into conduction, defining the direction from the positive electrode of the external power source to the positive input terminal of the electric load as a forward direction, a third diode that brings the positive electrode of the external power source and the positive electrode of the battery into conduction, defining the direction from the positive electrode of the external power source to the positive electrode of the battery as a forward direction, and a circuit that brings the negative electrode of the external power source, the negative electrode of the battery, and the negative input terminal of the electric load into conduction, and an output electric power controller that sets an output voltage of the external power source to be higher than a total voltage of a voltage across electrodes of the battery when the battery is fully charged and a forward voltage of the third diode, while setting a current of the external power source that can be output to be larger than a required current of the electric load.