A gas-liquid separator includes a cylindrical inlet pipe and a fluid inflow pipe. The inlet pipe includes a fluid inlet which is formed in a fluid entering side and radially opens. An axis line of the inlet pipe horizontally extends. The fluid inflow pipe includes at an end a connection opening connected to the fluid inlet. An axis line of the fluid inflow pipe horizontally extends. The fluid inflow pipe introduces the gas-liquid two-phase fluid through the fluid inlet from a side of the inlet pipe. In a connecting portion, a position of an axis line extending through a center of a connection opening in communication with the fluid inlet is vertically offset with respect to a position of the axis line of the inlet pipe.