To prevent a lock on the interior side from being illegally unlocked from the outside so as to improve a theft preventing property during a bedtime or in the case of absence.

This fitting is provided with a frame body 1 constructed of an upper frame 1a, a lower frame 1b and lift and right vertical frames 1c, 1d, inside and outside sashes 4, 5 arranged freely openably and slidably in the opposite directions inside the frame body 1, and a meeting lock 10 arranged in the meeting part between the sashes 4, 5. The meeting lock 10 is provided with cylinders 11, 12 locked/unlocked in both of the outside sashes 4, 5 by key operation, and a key 13 with a latch 13a is installed in the inside sash side cylinder 12 usually. When the key 13 with the latch is moved upward/downward, the inside sash side cylinder 12 is locked/unlocked via a connecting member 14, and when the key 13 is turned, connection with the connecting member 14 is released, while the key 13 with the latch can be removed.