A lock mechanism for a stage apparatus, the stage apparatus having a stationary support board and a movable stage, includes a lock member positioned immediately in front or behind the movable stage; lock holes formed in opposed portions of one of the lock member and the movable stage; lock pins formed on the opposed portions of the other of the lock member and the movable stage, wherein ends of the lock pins which are smaller in diameter are engageable and disengageable from the lock holes; and a driving device which moves the lock member toward the movable stage to engage the lock pins with the lock holes upon the movable stage entering a non-operational state, and moves the lock member away from the movable stage to disengage the lock pins from the lock holes upon the movable stage entering an operational state.