A conveyance device has a carriage drive for driving and propelling a pair of left and right carriage units which individually support left and right sides of an object to be conveyed. A pair of left and right screw shafts is pivotally supported in a rotatable manner along the movement path of the carriage units. Driven rollers are pivotally supported in a rotatable manner by the carriage units and engage with the screw shafts. A transmission connects the pair of left and right screw shafts through the outside of a conveyance path such that the left and right screw shafts are linked and coupled; and a single motor drives the pair of left and right screw shafts through the transmission means.