To prevent a pivotal shaft of a folding door from slipping off of a lower rail even when a panel is pushed up.

A latch device is constituted of an A piece 25 and a B piece 30. The A piece 25 is elastically connected and disconnected to and from an upper pin to be a pivotal shaft of a panel which is projected between a panel upper end of a folding door and an upper rail by cutting one side open. The B piece 30 can slide in the axial direction by engaging a side edge 31 with a groove 28 of the A piece 25. At this time, it is possible to move the B piece 30 only in a direction to project from the A piece 25 due to engagement of teeth formed on both of the A and B pieces and inclinations on both sides of which effectively changed.