Stage devices are disclosed that include gas-actuation and reaction-force-canceling mechanisms. In an embodiment, an X-axis moving guide extending in the X direction engages a lower stage via a gas bearing. Y-axis sliders (movable elements) are provided at both ends of the X-axis moving guide. A Y-axis fixed guide 8 engages each Y-axis slider via a gas bearing. Each Y-axis slider and respective fixed guide constitute a respective pneumatic actuator. Respective mounting members are provided near the ends of each fixed guide, with interposed gas bearings, and each fixed guide is slidably affixed to a base plate. An actuator for stroke correction is provided in association with each mounting member.