1. A periphery monitoring device for a work machine, comprising: a plurality of imaging devices that each captures an image of surroundings of the work machine; an overhead view image generating unit that converts the image captured by each of the plurality of imaging devices into an upper view-point image, and generates an overhead view image of the surroundings of the work machine based upon upper view-point images; and a display unit that displays the overhead view image in an overhead view image display region, wherein: when generating an overhead view image of an overlap region of a first upper view-point image relating to the image captured by a first imaging device included in the plurality of imaging devices and a second upper view-point image relating to the image captured by a second imaging device included in the plurality of imaging devices; the overhead view image generating unit, based upon a height of a virtual monitoring target, sets at least one of a first region in which the first upper view-point image is displayed and a second region in which the second upper view-point image is displayed, and also sets a third region in which a composite display image based upon the first and second upper view-point images is displayed.