A gas sampling bag is capable of blowing out the gas uniformly into the bag main body, and filling the bag main body with gas in a securely mixed state. A gas sampling bag that is connected to a constant volume sampling passage, contains a pipe, on which a plurality of gas inlet/outlet holes are formed, in a bag main body, and allows the gas to flow into/out of the bag main body through the gas inlet/outlet holes. The opening of the plurality of gas inlet/outlet holes is formed in such a manner that the size is minimized while the pressure loss is suppressed so as not to increase as far as possible.