A heat transfer medium supply system includes valve units each alternately supplying a first and a second heat transfer medium to a corresponding zone of a stage. The valve unit includes a housing and a shaft. The housing has first and second inlets, and first and second outlets. The first and second inlets are respectively connected to a first and a second medium temperature controller. The first and second outlets are connected to the corresponding zone. The shaft is inserted in the housing and has first and second supply grooves. The first supply groove connects the first inlet to the first outlet when a rotation angle about a central axis of the shaft is within a first angle range, and the second supply groove connects the second inlet to the second outlet when the rotation angle about the central axis of the shaft is within a second angle range.