An opening movement control device of a sliding door on a vehicle body. The sliding door having an outer panel connected to an inner panel to define a space therebetween, with a window glass slidably supported between the panels. A link mechanism disposed in the space includes a drive link coupled to the glass to cause reciprocal motion thereof. A drive shaft is rotatably supported by a module base, with one end passing through the module base, and another end fixed to the drive link. A cam member is fixed on the one end of the drive shaft, and a cam follower is movably supported by the inner panel and contacting the cam member. A stopper coupled to the cam follower contacts the vehicle body only when the glass moves down to prevent movement of the door when the window glass is down.