PROBLEM TO BE SOLVED: To easily switch the detection sensitivity of a sensor, in a constitution for detecting upper and lower positions of a body to be detected which contacts with mud and vertically moves by the sensor.SOLUTION: A rice field working machine comprises a transmission member 68 which connects an oscillating arm 64 for supporting a grounding member 65 which sinks into the mud of a field, and a working member 67 which oscillates integrally with an operation shaft part 66A of a mud sensor 66. A connecting position adjusting part F having a plurality of engagement holes 67A formed at the working member 67 is arranged so as to change a position in which the transmission member 68 is connected to the working member 67.【課題】泥土に接触して上下動する検知体の上下位置をセンサで検出する構成においてセンサの検知感度を容易に切り換えるように構成する。【解決手段】圃場の泥土に沈み込む接地部材６５を支持する揺動アーム６４と、泥土センサ６６の操作軸部６６Ａと一体的に揺動する作動部材６７とを結ぶ伝達部材６８を備え、作動部材６７に伝達部材６８が連結する位置の変更を可能にするように、作動部材６７に形成した複数の係合孔６７Ａを有する連結位置調節部Ｆを備えた。【選択図】図１１
