NOVELTY - The apparatus (1) has water supply unit (30) that supplies water (W) to one end portion of water distribution line (L3). A mixing discharge portion (41-44) is provided in connection position of fuel mixing line (L2) and water distribution line, for mixing fuel gas (G1) and water. A control unit (50) is provided to perform control operation for changing the number of objects of switching portion (21-24) which connected with branch line portion (LD1-LD4) according to supply amount of the fuel gas to fuel distribution line (L1) with respect to each switching portion.    USE - Apparatus for supplying fuel gas to modifier, used in fuel cell system.    ADVANTAGE - The fuel gas and water of more optimal Steam/Carbon (S/C) value can be supplied to modifier. The supply of water to ejector can be suppressed when the switching valve is a closed state. The blocking of each branch line portion can be realized by simpler structure. The reforming reaction of the mixed fluid can be promoted more efficiently. The fuel gas and the water can be mixed efficiently, without providing the mechanism for mixing the fuel gas and the water.    DETAILED DESCRIPTION - The fuel distribution line on which fuel gas can flow in from one end portion, and other end portion side is comprised with branch line portion. A fuel supply unit (10) is provided to supply the fuel gas of predetermined amount to the one end portion of the fuel distribution line. A switching unit is respectively connected to each edge portion of the branch line portion. A fuel mixing line is provided to connect each switching portion and modifier (70) respectively. A water distribution line on which water can flow in from one end portion, and is respectively connected to end portions of fuel mixing lines. The mixing discharge portion is comprised as an ejector. All the quantity of the mixed fluid of the fuel gas and water are discharged from the ejector. The mixed fluid of the fuel gas and water which are discharged from the ejector is heated with a heater (60). Each switching portion is comprised as valve.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic block diagram of the fuel gas supply apparatus.    Fuel gas supply apparatus (1)    Fuel supply unit (10)    Switching portion (21-24)    Water supply unit (30)    Mixing discharge portions (41-44)    Control unit (50)    Heater (60)    Modifier (70)    Fuel gas (G1)    Fuel distribution line (L1)    Fuel mixing line (L2)    Water distribution line (L3)    Branch line portions (LD1-LD4)    Water (W)