A substrate treating apparatus comprising: a plurality of substrate treatment lines (Lu, Ld) configured to treat substrates, each line including a plurality of main transport mechanisms arranged horizontally, and a plurality of treating units (31, 41) associated with each of the main transport mechanisms; wherein each of the substrate treatment lines (Lu, Ld) is carrying out a series of treatments on the substrates, with each of the main transport mechanisms transporting the substrates to the treating units associated therewith, and transferring the substrates to another main transport mechanism positioned horizontally adjacent thereto; wherein the plurality of substrate treatment lines (Lu, Ld) are arranged vertically; characterized in that an atmosphere of transporting spaces where the main transport mechanisms are installed is blocked off for each of the substrate treatment lines (Lu, Ld); each of the substrate treatment lines (Lu, Ld) includes: blowout units, each blowout unit being in form of a flat box having substantially the same area as that of each of the transporting spaces, and having gas supply openings (61 a) in form of numerous small bores formed in one surface thereof and directed downward for supplying a gas into the transporting spaces; and exhaust units, each exhaust unit being in form of a flat box having substantially the same area as that of each of the transporting spaces, and having gas exhaust openings in form of numerous small bores formed in one surface thereof and directed upward for exhausting the gas from the transporting spaces; the gas supply openings of each transporting space are arranged in a position higher than the gas exhaust openings of the each transporting space; the atmosphere of each of the transporting spaces is blocked off for each of the substrate treatment lines (Lu, Ld) by one of the blowout units and one of the exhaust units; and the series of treatments carried out in each of the substrate treatment lines (Lu, Ld) is the same. a plurality of substrate treatment lines (Lu, Ld) configured to treat substrates, each line including a plurality of main transport mechanisms arranged horizontally, and a plurality of treating units (31, 41) associated with each of the main transport mechanisms; wherein each of the substrate treatment lines (Lu, Ld) is carrying out a series of treatments on the substrates, with each of the main transport mechanisms transporting the substrates to the treating units associated therewith, and transferring the substrates to another main transport mechanism positioned horizontally adjacent thereto; wherein the plurality of substrate treatment lines (Lu, Ld) are arranged vertically; an atmosphere of transporting spaces where the main transport mechanisms are installed is blocked off for each of the substrate treatment lines (Lu, Ld); each of the substrate treatment lines (Lu, Ld) includes: blowout units, each blowout unit being in form of a flat box having substantially the same area as that of each of the transporting spaces, and having gas supply openings (61 a) in form of numerous small bores formed in one surface thereof and directed downward for supplying a gas into the transporting spaces; and exhaust units, each exhaust unit being in form of a flat box having substantially the same area as that of each of the transporting spaces, and having gas exhaust openings in form of numerous small bores formed in one surface thereof and directed upward for exhausting the gas from the transporting spaces; the gas supply openings of each transporting space are arranged in a position higher than the gas exhaust openings of the each transporting space; the atmosphere of each of the transporting spaces is blocked off for each of the substrate treatment lines (Lu, Ld) by one of the blowout units and one of the exhaust units; and the series of treatments carried out in each of the substrate treatment lines (Lu, Ld) is the same. blowout units, each blowout unit being in form of a flat box having substantially the same area as that of each of the transporting spaces, and having gas supply openings (61 a) in form of numerous small bores formed in one surface thereof and directed downward for supplying a gas into the transporting spaces; and exhaust units, each exhaust unit being in form of a flat box having substantially the same area as that of each of the transporting spaces, and having gas exhaust openings in form of numerous small bores formed in one surface thereof and directed upward for exhausting the gas from the transporting spaces; the gas supply openings of each transporting space are arranged in a position higher than the gas exhaust openings of the each transporting space; the atmosphere of each of the transporting spaces is blocked off for each of the substrate treatment lines (Lu, Ld) by one of the blowout units and one of the exhaust units; and the series of treatments carried out in each of the substrate treatment lines (Lu, Ld) is the same.