To prevent the production efficiency degradation of an electronic component mounting device by seizing a component placement region on a conveyor for the electronic component mounting device so that defective components are efficiently filled and placed in an empty region on the conveyor, while minimizing the interruption of production due to the collection of components.

The electronic component mounting device includes a substrate carrying device for carrying substrates, a component transfer device movably supported in two X- and Y-directions for sampling components supplied by a component supply device and mounting them on the substrates on the substrate carrying device, and a component carrying-out device having the conveyor for carrying out the components determined to be defective. Herein, the empty region in the component placement region set on the conveyor, where the components are not placed, is seized so that the defective components are filled and placed in the empty region in consideration of the directions and arrangement sites of the defective components when the components sampled by the component transfer device are determined to be defective.