FIG. 1 is a front elevational view of the gas filling apparatus of the present invention showing our new design; FIG. 2 is a rear elevational view thereof; FIG. 3 is a right side elevational view thereof; FIG. 4 is a left side elevational view thereof; FIG. 5 is a top plan view thereof; FIG. 6 is a bottom plan view thereof; and, FIG. 7 is a top, front perspective view thereof.