PURPOSE: To perform a transfer operation of platelike parts steadily, even if there is an error in the pitch of retainer grooves in a cassette, by inching platelike parts in small steps or at low speed.

CONSTITUTION: A controller 28 controls a motor 27 to drive a feed screw 25 that engages a female screw 24 to lower a carriage 23 by a 1/2 pitch to a height of T2. Then, the carriage is lowered by a 1/6 pitch by means of the feed screw and female screw, and a counter is incremented. Since wafers 11 in a cassette 12 on the carriage are lowered by a 1/6 pitch every time near its normal position T5 in this manner, a suction head 38 can steadily hold a wafer even if there is an error in the pitch of retainer grooves in the cassette.