To improve a function by arranging a rotary body to rotate along a braking starting part arranged in a guide groove and a rotary body braking means, in a door to move along the guide groove.

Through a casing 21, a braking case 24 is installed on a sliding door 3 to move along a guide groove 23 of a guide rail 22, and a gear 26 to rotate along a flat tooth-shaped braking starting part 25 arranged in a prescribed position of the groove 23 and a resistance imparting means 27 to impart rotational resistance to the gear 26, are arranged inside of it, and a braking device is constituted. A means 27 is formed of, for example, a sealing case 27A in which highly viscous oil is sealed and a resistance blade 27B to rotate in it. When a door 3 approaches a closing position or a maximum opening position, the gear 26 rotates by contacting with the starting part 25, and rotational resistance by the means 27 brakes travel of the door. Therefore, a braking characteristic can be changed by adjusting a length of a braking starting part according to a sevice condition, and impact force is reduced, and durability can be improved, and since the casing is arranged, a braking member can be efficiently installed.