PROBLEM TO BE SOLVED: To provide a lawn mower capable of simplifying a supporting structure for supporting a boundary detector, as well as capable of accurately detecting a mowing track boundary between a mowed area and an unmowed area by a boundary detector.SOLUTION: The lawn mover includes: a mower 4 which mows the lawn following the running of a running machine that is run and driven by running driving devices 11R, 11L to go straight and turn； a boundary detector Q for detecting the mowing track boundary between the mowed area and the unmowed area； and a control means for performing a predetermined control for running based on the detection information of the boundary detector Q. The boundary detector Q detects whether or not the lawn exists in front of a front side longitudinal wall part 7B1 in a cutting blade housing 7 of the mower 4.
