A stage apparatus enables easy position alignment at a real installation site. Mounts 25 having sub base plates 21 arranged thereon are provided on carriages 25 and thereby constitute sub mounting tables 20a to 20d; and the mounts 25 are fixed to a main mounting table 10 having a main base plate 11. The positions of main base plate 11 and sub base plates 21 are aligned with each other by adjustment mechanisms 30 provided on the sub mounting tables 20a to 20d. As main positioning members 16 and sub positioning members 241, 242 are arranged on the main mounting table 10 and sub mounting tables 20a to 20d, separation can be performed so that a state of position alignment is restorable. Accordingly, position alignment is easy when assembling after transportation.