A substrate treatment system comprise a treatment station having a plurality of treatment units provided at multiple tiers in an up-down direction, a cassette mounting table on which a cassette housing a plurality of wafers W is mounted, and a wafer transfer mechanism arranged between the treatment station and the cassette mounting table, wherein a delivery block in which a plurality of delivery units are provided at multiple tiers is provided between the treatment station and the wafer transfer mechanism, the delivery units temporarily housing a wafer to be transferred between the cassette mounting table and the treatment station and a wafer to be transferred between the tiers of the treatment units. The wafer transfer mechanism includes a first transfer arm that transfers a wafer between the cassette mounting table and the delivery block, and a second transfer arm that transfers a wafer between the tiers of the delivery units.