With this type of retracting device, when a sliding door is moved manually along a guide rail in a closing direction or an opening direction, a biasing force in the closing direction or the opening direction by a biasing member such as a coil spring is exerted on the sliding door at a certain point.  The sliding door moves automatically to a fully closed position or a fully open position by the biasing force of the biasing member. 
In Patent Literature 1, a retracting device that assists closing and opening of a sliding door is disclosed.  A guide rail extending in opening and closing directions of the sliding door is mounted to a ceiling.  The retracting device is received in the guide rail and can slide in the guide rail in a longitudinal direction by rollers.  The sliding door suspends from the retracting device.  There are a first pin and a second pin attached to the guide rail.  The retracting device is provided with a first slider which can catch the first pin and a second slider which can catch the second pin. 
When the sliding door is moved manually in the closing direction or the opening direction, the retracting device also moves with the sliding door in the closing direction or the opening direction.  When the sliding door is moved manually in the closing direction and the retracting device is moved in the closing direction and reaches a certain point of the guide rail, the first slider of the retracting device for assisting the closing catches the first pin.  Then, lock of the first slider with the retracting device is released and the retracting device moves automatically in the closing direction due to a biasing force of a biasing member and the sliding door suspending from the retracting device moves automatically to a fully closed position.  When the sliding door is manually moved in the opening direction, in the same way as in closing of the sliding door, the second slider for assisting the opening catches the second pin at a certain point and the sliding door moves automatically to a fully open position due to the biasing force of the biasing member. 
In the retracting device described in Patent Literature 1, a linear damper is provided over between the first slider and the second slider in order to cushion impact when the sliding door is closed fully and opened fully.  In other words, an end portion of a damper main body of the linear damper is attached to the first slider and a tip end portion of a rod of the linear damper is attached to the second slider (see claim 1 of Patent Literature 1).