NOVELTY - The exhaust gas drain valve has an internal-diameter gradual variation portion (85v) whose internal diameter becomes small gradually toward a valve opening side and is connected with a valve segment storage chamber through an inflow flow path (85d). A level difference surface (85p) is formed as an annular surface that extends in a direction orthogonal to a formation direction of orifice holes (85f), and follows a circumferential direction. The level difference surface is formed between the internal-diameter gradual variation portion and orifice holes.    USE - Exhaust gas drain valve used in fuel cell system for emitting water produced by fuel cell such as solid polymer type single cell with fuel gas such as hydrogen gas.    ADVANTAGE - Since the cross-sectional area of an inflow flow path becomes small in an orifice hole, at the time of release of an exhaust gas drain valve, the flow rate of the gas which distributes an inflow flow path is accelerated in an orifice hole. Thus the moisture content adhering to the internal peripheral surface of the orifice hole is purged and removed by the gas by which the flow rate was accelerated. Since the moisture content cannot remain easily in an orifice hole, even when it is a low temperature environment below sub-zero temperature, the obstruction in the inflow flow path resulting from freezing of the moisture content in an inflow flow path can be suppressed. Since the water droplet flowed down to a level difference surface side is transmitted to the recessed portion groove formed in the circumference of an orifice hole and flows down below from the ceiling portion of an internal-diameter gradual variation portion, the penetration into the orifice hole of a water droplet can be suppressed.    DESCRIPTION OF DRAWING(S) - The drawing shows the figure schematic perspective view illustrating the communication portion of the internal-diameter gradual variation portion and an orifice hole of the exhaust gas drain valve.    Inflow path (85d)    Large diameter flow path (85e)    Orifice holes (85f)    Level difference surface (85p)    Internal-diameter gradual variation portion (85v)