A device for automatically controlling the open-close of a vehicular sliding door enabling to smoothly change the slide door open-close control system from a manual to an automatic with decreasing any shock generated in changing the mode. Having a drive source (54), such as motor and the like, a slide door (3) able to open and close by the manual or the slide door open-close mechanism, a clutch (56) for conveying intermittently drive force of the drive source to the slide door open-close mechanism, a door speed detector (78), and a slide door controller (7) for controlling the drive source and the clutch in order to adjust the drive force transferred to the slide door open-close mechanism. When the slide door is detected that it is moving at a speed higher than a manual recognition speed, the drive source and the slide door open-close mechanism are connected at a half-clutched condition and then they are connected at a full-clutched condition.