A plurality of nozzles are arranged at intervals of a center-to-center distance along a circumferential orbit around the predetermined rotation axis integrally. The nozzle that is positioned at the working position is changed by rotating the plurality of nozzles around the predetermined rotation axis. At that time, regardless of the manner in which the nozzle positioned at the working position is changed, the nozzle approaching the working position, and the nozzle moving away from the working position, move within an imaging target range having a width smaller than twice the center-to-center distance with the working position as the center along the circumferential orbit. Then, a camera images the nozzle which is moving within the imaging target range. Thus, it is not necessary to temporarily stop the nozzle for imaging, and as a result, imaging of the nozzles is performed efficiently.