In order to simplify work of applying and releasing a surface pressure in a slide valve device constructed of a fixed plate, a slide plate, a seal plate, and the like, provided is a slide valve device for automatic surface pressure application and a surface pressure application method therefor, the slide valve device including: a base frame (2) including a positioning member (51) for determining an arrangement location (X) of a seal case (21) and a stopper (52) for fixing the seal case (21) at the arrangement location (X); and a slide case (4) including a pusher (53) for sliding the seal case (21) together with the slide case (4) when sliding the slide case (4) in a surface pressure application direction.