A substrate conveyor track is provided with first to fourth conveyors. Two conveyors situated on both sides of the substrate conveyor track, and the other two conveyors situated at the center of the same. There is enabled selection of any one from a small substrate mounting mode for giving a single substrate conveyance width to the four conveyors and mounting electronic components on four small substrates having the single width; a large substrate mounting mode for actuating all movable conveyors to the center of the substrate conveyor track and mounting electronic components on two large substrates by the two conveyors; and a large-small-substrates mounting mode for bringing the two conveyors on one side of the substrate conveyor track, among the four conveyors, into the small substrate mounting mode and bringing one of the conveyors on the other side of the track into the large substrate mounting mode.