A gas liquid separator (1A, 1B, 1C, 1D, 1E, 1F, 1G) comprising: a sealed container comprising: an upper cover portion; a tubular portion that allows the liquid layer to flow down along an inner peripheral face of the tubular portion; and a lower cover portion that retains the liquid layer to form a liquid reservoir; a guide member that is disposed in the sealed container to form an inflow space between the guide member and the upper cover portion; a first pipe that extends through the guide member so that one end of the first pipe opens into the inflow space, and that is provided with a liquid outlet port in a portion submerged in the liquid reservoir; a second pipe that extends through the guide member so that one end of the second pipe opens into the inflow space, and that is provided with a liquid outlet port in a portion submerged in the liquid reservoir; and a gas outlet pipe for discharging, to the outside of the sealed container, a gas, wherein the first pipe and the second pipe are configured such that when one of the first pipe and the second pipe is used to introduce the gas-liquid two-phase fluid into the inflow space from outside the sealed container, the other one is used to discharge the liquid in the liquid reservoir to the outside of the sealed container through the liquid outlet port (31 or 32) of the other one while forming a liquid surface at a level above the liquid outlet port (31 or 32) and such that both the liquid outlet port of the first pipe and the liquid outlet port of the second pipe are located at a level below the liquid surface in the liquid reservoir, characterized in that the upper cover portion disperses an upward-injected gas-liquid two-phase fluid and directs the dispersed gas-liquid two-phase fluid downward so that a liquid contained in the gas-liquid two-phase fluid is pressed against an inner face of the upper cover portion and the gas-liquid two-phase fluid is converted into a two-layer flow including a liquid layer and a gas-rich layer; that the guide member forms a flow passage for the two-layer flow between the guide member and the inner peripheral face of the tubular portion; and guides the gas-rich layer down along the inner peripheral face of the tubular potion, that the gas being discharged by the gas outlet pipe, results from removal of a liquid from the gas-rich layer by surface tension of the liquid layer, and that the first pipe and the second pipe extend through the lower cover portion. a sealed container comprising: an upper cover portion; a tubular portion that allows the liquid layer to flow down along an inner peripheral face of the tubular portion; and a lower cover portion that retains the liquid layer to form a liquid reservoir; a guide member that is disposed in the sealed container to form an inflow space between the guide member and the upper cover portion; a first pipe that extends through the guide member so that one end of the first pipe opens into the inflow space, and that is provided with a liquid outlet port in a portion submerged in the liquid reservoir; a second pipe that extends through the guide member so that one end of the second pipe opens into the inflow space, and that is provided with a liquid outlet port in a portion submerged in the liquid reservoir; and a gas outlet pipe for discharging, to the outside of the sealed container, a gas, wherein the first pipe and the second pipe are configured such that when one of the first pipe and the second pipe is used to introduce the gas-liquid two-phase fluid into the inflow space from outside the sealed container, the other one is used to discharge the liquid in the liquid reservoir to the outside of the sealed container through the liquid outlet port (31 or 32) of the other one while forming a liquid surface at a level above the liquid outlet port (31 or 32) and such that both the liquid outlet port of the first pipe and the liquid outlet port of the second pipe are located at a level below the liquid surface in the liquid reservoir, that the guide member forms a flow passage for the two-layer flow between the guide member and the inner peripheral face of the tubular portion; and guides the gas-rich layer down along the inner peripheral face of the tubular potion, that the gas being discharged by the gas outlet pipe, results from removal of a liquid from the gas-rich layer by surface tension of the liquid layer, and that the first pipe and the second pipe extend through the lower cover portion.