first slots 142 and then vertically move to load the plurality of wafers 112 in the first slots 142 as illustrated in fig7 c the first boat 140 is raised so that the first slots 142 storing the plurality of wafers 112 become approximate to the second slot 152 positioned above the first slot 142 here the plurality of wafers 112 stored in the first slots 142 are raised a given height by a movement of the first boat 140 thereby substantially reducing the interference between the plurality of wafers 112 stored in the first slots 142 and the plurality of wafers 112 to be loaded on the second slots 152 for example the first slot 142 may be raised to a height level of about 4 mm the raised distance of the first slot 142 may become a space where the plurality of wafers 112 to be subsequently loaded in the second slots 152 horizontally move and then vertically move by the blade 160 of the transfer robot thus the plurality of wafers 112 subsequently inserted between the plurality of wafers 112 loaded in the first slots 142 of the first boat 140 can be loaded in the second slots 152 of the second boat 150 without a collision as shown in fig7 d the transfer robot rotates about 180 degrees the plurality of wafers 112 and loads the wafers so that the front faces 112 a of the plurality of wafers 112 are loaded in the second slots 152 that is the transfer robot horizontally moves the plurality of wafers 112 from wafer cassette in a state that.