Abstract: A fluid containing bag according to the invention includes a bag main body which is constituted by front and rear two sheets and an entire periphery of which is hermetically sealed except one portion, an inlet/outlet spout one end side of which is connected to the one portion and other end side of which is extended to outside of the bag main body, means for closing an inlet/outlet port of the inlet/outlet spout, and a reinforcing tape attached to a portion or an entire periphery of an inner peripheral face of the bag main body connecting side base portion of the inlet/outlet spout.