A plurality of conveyors including a center conveyor are appropriately disposed without any gap or step and any interference between driving units. The center conveyor includes a pair of left and right belt driving pulleys that are provided at the front and rear sides in the conveying direction so as to stretch loop-shaped conveyor belts therebetween and are provided at both sides in the width direction, a pair of first left and right pulleys that is connected to each other through a connection shaft disposed on rotation axes of the belt driving pulleys at both outer sides in the width direction, a pair of left and right second pulleys that is provided below the first pulleys at both outer sides in the width direction so as to stretch loop-shaped pulley belts between the first and second pulleys and includes a common rotation axis, a driving shaft that is disposed on rotation axes of the second pulleys and is connected to the pair of second left and right pulleys, and a motor that is connected to an end of the driving shaft.