A lock mechanism for a stage apparatus includes a movable stage; a pair of engaging members provided on the movable stage; a pair of lock members positioned between the engaging members and movable along an imaginary straight line passing through the engaging members; a first link member movable along a reference straight line between the lock members; a pair of second link members rotatably mounted on the first link member and rotatably mounted on the lock members; a lock driving device which moves the lock members mutually away from each other to engage with the engaging members by moving the first link member along the reference straight line; and an unlock driving device which moves the lock members mutually toward each other so as to disengage with the engaging members by moving the first link member in the other direction along the reference straight line.