There is provided a screen printer capable of concurrently, efficiently subjecting a plurality of substrates, including different types of substrates, to printing operation. In a screen printer 2 that makes up an electronic component mounting line 1 and that prints electronic component bonding paste on a substrate, a substrate conveyance section 8 that conveys a substrate 5 forwardly or backwardly in a direction of conveyance of a substrate is disposed at an intermediate position between a first screen printing section 7A and a second screen printing section 7B 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 5 from a downstream machine to an upstream side of the screen printer 2 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. The plurality of substrates 5, including different types of substrates, can concurrently, efficiently undergo printing operation.