Abstract: A lifting device for pivotally raising a prefabricated wall section from a substantially horizontal position to a vertical position on the floor of a building under construction comprising a trolley having a frame, a pair of spaced rollers mounted for rotation thereon and defining an opening for receipt and passage therethrough of an elongated beam with the rollers in frictional, gripping engagement with the beam, motors mounted on the frames in operative driving engagement with the rollers, and a hinge pivotally mounted on the frame for attachment to the ultimate upper end portion of a prefabricated wall section to permit pivotal movement of the hinge about its point of attachment to the frame during wall-lifting operations. The trolley travels along the beam as the beam pivots on the floor of the building from vertical to diagonal position during corresponding pivotal movement of the prefabricated wall from horizontal to vertical position.