To provide an improved means to endure external force at a very low temperature, reduce penetration of heat into a plurality of bags placed together from a high environmental temperature, reduce necessary storage space for the plurality of bags, and make the cross section of the bag thin and substantially uniform so that penetration and emission of heat are almost uniform along the whole content of the bag for protecting activity of living cells during freezing and thawing.

The freezing bag for medical use is provided with a first bag part and a second bag part. A first outer edge part 6 and a second outer edge part 6 are joined with each other to form an end wall 2 that is round, which has such breakage resistance to be durable to phase change of liquid in the bag during freezing and thawing.