An apparatus for connecting two double vacuum pipes for conducting cryogenic fluid consists of a tubular connecting mechanism connected to the outer tube of a double vacuum pipe by a tubular member, a one-touch locking mechanism connected to the outer tube of the other double vacuum pipe by another tubular member inserted in the first-mentioned tubular member, a warming chamber defined between both tubular members, valve mechanisms respectively provided between the tubular members and the inner tubes of the double vacuum pipes which valve mechanisms cooperate to close the inner tubes of the respective double vacuum pipes at the closed position so as to make the inner tube of one of the double vacuum pipes communicate with the warming chamber during the connection of both the double vacuum pipes and to cause the inner tubes of both double vacuum pipes to communicate with each other. During the connection of both double vacuum pipes, cryogenic liquid is introduced in the warming chamber to be evaporated and its temperature is raised to avoid generation of frost on the to-be-connected portions of the double vacuum pipes. A one-touch locking mechanism provides quick connection and disconnection of the double vacuum pipes.