Pipe coupling used with automatic connecting and disconnecting device

A pipe coupling used with an automatic connecting and disconnecting device, comprising a cylindrical first main body having a connection opening in a front end face thereof, a second main body having a front end portion of an outer diameter which can fit in said connection opening and a second valve hole in a front end face thereof, said first and second main bodies arranged to face each other on a common axis and adapted to allow mutual approaching and departing movement, a valve seat disposed in said first main body and urged against said connection opening by a first spring, said valve seat having a first valve hole in a front end wall thereof and being slidable along said axis, a first check valve of a small diameter adapted to close said first valve hole of said valve seat from the outside thereof, a second check valve of a large diameter adapted to be urged by a second spring to close said second valve hole of said second main body from the inside thereof, and an annular sealing member disposed on one of the front end face of said valve seat and the front end face of said second main body, characterized in that said coupling further comprises a passageway for connecting a specific area of said front face of said first main body which is enclosed by said annular sealing member when both said main bodies are put in contact to the interior cavity of said first main body, and a third check valve disposed in said passageway for inhibiting fluid in said interior cavity from flowing out through said passageway into said specific area.