A transfer pathway of a mounting head 10 in a component-mounting round during which the mounting head 10 moves back and forth between a component feeding unit 4 and a substrate conveyance mechanism 2 is derived by a transfer pathway calculation unit 25 for each component-mounting round from mounting program data 21a. A focusing processing unit 24 controls an optical system focusing mechanism 18, thereby matching a focusing point of a line sensor camera 14 achieved during imaging operation to the transfer pathway of the mounting head 10 based on data pertaining to the derived transfer pathway. Further, an optical system zooming mechanism 17 adjusts an imaging range according to the focusing point. Accordingly, even when a long substrate 3 is taken as an object, it is possible to detect with high precision whether or not a component exists on the pickup nozzle 11 of the mounting head 10.