A drug discovery screening apparatus improves a testing operation efficiency. The drug discovery screening apparatus comprises an image measurement unit, an incubator unit integrally connected to the image measurement unit, a fixed stage disposed at the incubator unit, first conveyance for taking out one of plates stored in a carousel of the incubator unit and conveying the plate onto the fixed stage, second conveyance for taking out the plate conveyed onto the fixed stage and conveying the plate onto an XY stage disposed at the image measurement unit, and a control unit. The second conveyance comprises first and second conveyance arms, respectively supported horizontally by a conveyance unit support section, which convey the plates onto the fixed stage and XY stage so as to allow the respective plates to cross each other.