A challenge to be met by the present invention is to provide a component mounting device, a component mounting system, and a component mounting method that make it possible to correctly position a substrate at a working location and mount components on the substrate even when components mounted on the substrate project outside from an end of the substrate in a direction parallel to a substrate conveyance path. When a front end portion (PbT) of a substrate (Pb) conveyed by a substrate conveyance path (13) is detected to have reached inspection light (L), operation of the substrate conveyance path (13) is immediately halted. When a front end portion (PtT) of a projecting portion H of a component (Pt) mounted on the substrate Pb is detected to have reached the inspection light (L), the substrate conveyance path (13) is activated in such a way that the substrate (Pb) moves in the direction of projection of the projecting portion (H) over a distance equivalent to a projection length (α) of the projecting portion (H) reached the inspection light (L) and is subsequently stopped, thereby positioning the substrate (Pb).