A blower apparatus comprises a box-like main frame provided with a main-frame inlet port and a main-frame outlet port in positions confronting each other, and a plurality of centrifugal blower units for suctioning through a blower inlet port air taken inside of the main frame from the main-frame inlet port and discharging the air from a blower air outlet toward the main-frame outlet port. The main frame is provided with a maintenance opening in one of the surfaces other than the surfaces having the main-frame inlet port and the main-frame outlet port for the purpose of checking the inside of the main frame, and the plurality of centrifugal blower units are disposed one another in a direction toward the maintenance opening so that a difference in discharging spatial distances from the blower air outlets of the adjoining centrifugal blower units to the main-frame outlet port is equal to or greater than an outer diameter of an impeller of the centrifugal blower unit located nearest to the maintenance opening.