NOVELTY - An on-demand hydrogen gas generation device (10) comprises cell with mechanism (22) for generating average flow of hydrogen gas of greater than or equal to 0.1 cm3/minute/cm3 of fuel volume for greater than or equal to 1 hour, and switching mechanism for regulating generation of hydrogen gas in cell. The switching mechanism includes movable unit operable to repeatedly move between first position and second position in response to pressure differential created by cell of less than 30 psig.    USE - An on-demand hydrogen gas generation device for use in fuel cell.    ADVANTAGE - The device utilizes water electrolysis and galvanic cell corrosion and/or chemical hydride reaction to produce hydrogen gas for fuel cell consumption; desirably generates and releases flow of hydrogen gas at constant pressure; and provides gas management system designed to maximize the release or evolution of hydrogen gas, thus maximizing hydrogen gas output.    DETAILED DESCRIPTION - On-demand hydrogen gas generation device (10) comprises cell with mechanism (22) for generating average flow of hydrogen gas of greater than or equal to 0.1 cm3/minute/cm3 of fuel volume for greater than or equal to 1 hour; and switching mechanism in communication with cell, regulating generation of hydrogen gas in the cell. The switching mechanism includes movable unit operable to repeatedly move between first position and second position in response to pressure differential created by cell of less than 30 psig. In first position, an electrical current passes through switching mechanism which enables generation of hydrogen gas from cell. In second position, resistance in switching mechanism to electrical current increases to reduce the rate of hydrogen gas generation within the cell.    DESCRIPTION OF DRAWING(S) - The drawing is a cross-sectional, schematic view of on-demand hydrogen gas generation device.    On-demand hydrogen gas generation device (10)    Negative end (18)    Generation mechanism (22)    Insulating wrap (55)