PROBLEM TO BE SOLVED: To reduce a work load of adjusting the length of a spray boom.SOLUTION: A pest control machine includes: a pair of left and right spray booms for spraying a chemical to a farm field a GPS reception part for receiving a radio wave transmitted from a GPS satellite and a control part for calculating a spray start position where the pest control machine starts spraying the chemical to the farm field on the basis of positional information of an area of the farm field where the chemical is sprayed, and a spray width, and adjusting a length of at least one of the pair of left and right spray booms based on at least the chemical spray start position when the pest control machine is determined to have reached the chemical spray start position from the positional information of the pest control machine acquired by the GPS reception part. When determining that the pest control machine have passed the chemical spray start position, the control part corrects the chemical spray start position, corrects the spray width of the chemical, and adjusts the length of the spray boom so as to be the corrected spray width.SELECTED DRAWING: Figure 2
