In this day and age, Japan's farming population is declining, and the farm workers are aging. For elderly farmers, the task of weed control is difficult. Especially in the summer when the temperature rises, it is a big burden. In recent years, the robotization of mowing work has been promoted for the safety and lightening of the work on the side slope. From this situation, the Ministry of Agriculture, Forestry and Fisheries is proposing and promoting "smart agriculture", which is a new type of agriculture that aims to save labor and improve work safety by letting robots perform weeding on the Levee slope. The purpose of this paper is to find the most suitable position for the outrigger arm to suppress robot slip through experimental investigation of the position relationship of the outrigger arm.