A flowing device for an optics-based methanol sensor includes an inner housing that surrounds the optics-based methanol sensor, an outer housing that surrounds the inner housing, a flow channel in the inner housing formed on a totally reflecting surface of the optics-based methanol sensor, a fuel inlet that is formed through the inner and outer housings and supplies liquid fuel to the flow channel, and a fuel outlet that is formed through the inner and outer housings and discharges the liquid fuel that has passed through the flow channel to an outside of the outer housing.