Transfer capability is improved without having to extend a longitudinal space of a platform of a cluster tool downward. In a platform PF, a first transfer robot 16L includes a transfer main body 48L that is slidable on a left guide rail 46L, a transfer pedestal 50L that is slidable in an offset direction (X direction), and a slider type transfer arm 52L that is rotatable within a horizontal surface while being movable straight in a direction parallel to a radius of a rotation circle and supports one piece of a semiconductor wafer W. A second transfer robot 16R has the same configuration and operations as the first transfer robot 16L except that an operation or moving direction of each component of the second transfer robot 16R is vertically symmetrical to that of the first transfer robot 16L.