A screen printer capable of concurrently, efficiently subjecting a plurality of different types of substrates, to a printing operation. The screen printer makes up an electronic component mounting line and prints electronic component bonding paste on a substrate. A substrate conveyance section that conveys a substrate forwardly or backwardly in a direction of conveyance of a substrate is disposed at an intermediate position between a first screen printing section and a second screen printing section arranged symmetrically with respect to a center line CL. It thereby becomes possible to adopt a variety of substrate conveyance forms, as required, such as return conveyance for returning the substrate from a downstream machine to an upstream side of the screen printer and bypass conveyance for letting the substrate sent from an upstream side pass through the screen printer, to thus be conveyed to a downstream machine.