1. A focus adjustment method using a working device that includes: a work table on which a substrate is placed; an image capture device not having an autofocus function; an XYZ drive device that moves the work table and the image capture device relative to each other; a storage device that stores images captured by the image capture device; a display device including an image display region that has a plurality of divided regions; an input device allowing arbitrary one of the divided regions in the image display region to be specified; an in-focus determination device that executes image processing on the plurality of captured images having been stored in the storage device, and that determines an in-focus image on the basis of contrasts of the captured images; and a control device that controls operations of the image capture device and the XYZ drive device, wherein the substrate is a substrate on which a plurality of objects having different heights are arranged on a surface of the substrate, and wherein the focus adjustment method comprises: a first step of obtaining a partial captured image in which a portion of the substrate is captured by the image capture device, and displaying the partial captured image in the image display region of the display device, wherein an image of a portion of the substrate is captured such that the captured image includes at least two of the objects; a second step of obtaining the plurality of captured images for a portion of the substrate corresponding to one divided region of the image display region, the one divided region being selected by a user through the input device, while the image capture device is moved in an up and down direction relative to the substrate, storing the plurality of captured images in the storage device, and causing the in-focus determination device to perform in-focus image determination on the captured images having been stored, wherein the captured images are continuously obtained while the image capture device is moved in the up and down direction relative to the substrate, the captured images are stored in the storage device together with coordinate values in the up and down direction at times when the images are captured, wherein those of the captured images in the one divided region selected by the user, which satisfy a determination reference value, are determined as in-focus images, and an in-focus identification flag is assigned to each of the captured images having been determined as the in-focus images; and a third step of displaying all of the captured images, which have been determined as the in-focus images and each assigned with the in-focus identification flag, in an arrayed state in the image display region.