a loader station of substrate treating apparatus receives a transport cassette from a preceding stage . this transport cassette stores a plurality of substrates to be treated , arranged with a predetermined spacing therein . an empty processing cassette stands by at the loader station when the transport cassette arrives . the processing cassette is constructed to store the plurality of substrates arranged with a storage spacing that is independent of the storage spacing in the transport cassette but is optimal for surface treatment in the apparatus . in the loader station , a loader substrate transport robot transfers the substrates to be treated from the transport cassette to the empty processing cassette while absorbing any difference that may exist between the storage spacings of the respective cassettes . after being emptied , the transport cassette is transported through a transport cassette buffer to an unloader station , the now loaded processing cassette is transported to the unloader station by way of a predetermined transport path having treating baths therealong for cleaning and drying the substrates in the processing cassette . in the unloader station , an unloader substrate transfer robot transfers the treated substrates from the processing cassette to an empty transport cassette while absorbing any difference there may be between the storage spacings of the respective transport and processing cassettes . after unloading of the treated substrates , the empty processing cassette is transported through a processing cassette buffer to the loading station for standby , and the transport cassette storing the treated substrates is transported from the apparatus to a next stage .