To obtain a closed lock state or a fully open enable state of doors by one operation of locking operation or unlocking operation.

A lock lever 10 having a lock piece inserted in a lock hole 7 provided on the door end 2' of an outer door 2 to be turned toward the inside and the outside of a room is rotatably assembled to the inside of the outer door 2. A catch hole which a piece of the lock lever 10 goes in and out is formed in one meeting style part 3' of an intermediate door 3 which laps the inside of the door trail end part 2" of the outer door 2. The each one end of a first and a second links 18, 19 are pivoted on a vertically movable piece 17 assembled to the inside of one meeting style part 3', and the other end of the first link is pivoted on the door end part 2' of the outer door 2 below the vertically movable piece 17. The other end of the second link 19 is pivoted on the door trail end part 2" of an inner door 4 which laps the inside of the other meeting style part 3" of the intermediate door 3 inside the vertically movable piece 17.