Abstract: Disclosed is a mechanism for allowing blood bags to communicate with each other comprising a connection pipe, a connection tube fitted into and bonded to said connection pipe, for connecting a first blood bag to a second blood bag, and a hard plastic-made communication pipe whose one end on the side of said first blood bag is hermetically sealed and the other end of which is fitted into and bonded to said connection tube and which is formed with a cutting-off small thickness section at its intermediate portion. The communication between said first and second blood bags is rendered effective by cutting off said communication pipe at said small thickness section.