To improve the function of a device by slidably inserting an engagement part of an outside sliding door and a vibration preventing part for inside sliding door into one longitudinal guide groove provided in a lower frame.

A double sliding sash 1 is formed of an upper frame 2, a lower frame 3, a vertical frame, a dressing room side sliding door 5 suspended inside of the frame 2, an intermediate sliding door 6, and a bath room side sliding door 7 provide outside. A longitudinal guide groove 31 is provided in the lower frame 3 at the bath room side, and the door 7 is arranged on the groove 31, and while a tight material is provided in a lower and of each door 5, 6, 7 at a dressing room side thereof so as to slide for contact on a top surface of the lower frame 3, and guide pins 53, 63, 73 respectively provided in the lower end of each door 5, 6, 7 are inserted into the grooves 31 freely to be rocked. With this structure, since each sliding door is suspended, they can be easily opened and closed, and since the only one guide groove is provided, stumbling on a nearly flat top surface of the lower frame and support by a wheel chair can be prevented, and the dust is hard to collect, and cleaning can be simply performed, and furthermore, even in the case where water is splashed to the door, since the water is cut by the guide groove, water leakage to the dressing room side can be prevented.