A wafer-processing apparatus includes: eight or ten reactors with identical capacity for processing wafers on the same plane, constituting four or five discrete units, each unit having two reactors arranged side by side with their fronts aligned in a line; a wafer-handling chamber including two wafer-handling robot arms each having at least two end-effectors; a load lock chamber; and a sequencer for performing, using the two wafer-handling robot arms, steps of unloading/loading processed/unprocessed wafers from/to any one of the units, and steps of unloading/loading processed/unprocessed wafers from/to all the other respective units in sequence while the wafers are in the one of the units.