NOVELTY - The hydrogen purification filter (1) has a porous support (2) with holes (3), and a palladium alloy film (4) joined to one surface (2a) of the support. The hole of the porous support has a shape with the narrowest portion (3a) inside. The support thickness, opening diameter of hole at film joining side, opening diameter of hole at opposite side, and opening diameter of narrowest portion satisfy preset relationships.    USE - For modifiers which carry out steam reforming of hydrocarbon group fuels and produce hydrogen-rich gas used as fuel in electric-power generating apparatuses, such as fuel cells (phosphoric acid fuel cell, molten carbonate type fuel cell, solid oxide fuel cell, alkaline fuel cell).    ADVANTAGE - The hydrogen purification filter has a palladium alloy film having excellent pinhole resistance and crack resistance. The filter has excellent hydrogen-permeation efficiency. Since the formation of metal film on palladium alloy film is not required, the manufacturing time of filter is shortened.    DETAILED DESCRIPTION - The hydrogen purification filter (1) has a porous support (2) with holes (3), and a palladium alloy film (4) joined to one surface (2a) of the support. The hole of the porous support has a shape with the narrowest portion (3a) inside.    The thickness (T) of the support, the opening diameter (D1) of the hole at the alloy-film joining side, the opening diameter (D2) of the hole at the opposite side, and the opening diameter (D3) of the narrowest portion of the hole satisfy preset relationships.    The sum total area of the opening of the hole at the alloy-film joining side is 20-80% of the s support area. The relationships are given by, D1/T = 1-5, D2/T = 1-5, D3/D1 is less than 0.8, D3/D2 is less than 0.9, and D3 is less than 250 microns.    An INDEPENDENT CLAIM is included for manufacture of hydrogen purification filter.    DESCRIPTION OF DRAWING(S) - The figure shows the fragmentary sectional view of the hydrogen purification filter.    hydrogen purification filter (1)    porous support (2)    surface (2a)    holes (3)    narrowest portion (3a)    palladium alloy film (4)