An apparatus that can supply oxyhydrogen gas includes an electrolysis device, a filter device, and a control device. The electrolysis device includes a voltage controller that applies voltages to positive and negative electrode plates to convert water electrolytically in an electrolysis chamber to form oxyhydrogen gas, which is outputted via a first output conduit. An output end of the first output conduit is extended below water level in a container of the filter device. A second output conduit permits the oxyhydrogen gas that flows through the first output conduit and through the water in the container to flow therethrough. The control device includes a ratio adjusting interface for controlling a difference in the voltages provided by the voltage controller so as to adjust a ratio of hydrogen to oxygen in the oxyhydrogen gas formed in the electrolysis chamber.