To perform a mowing operation efficiently by enabling a travel device to be operated at a speed and an output suitable for the mowing operation with excellent operability while avoiding increase in the size of a hydrostatic continuously variable transmission.SOLUTION: A hydraulic pump 60 and a hydraulic motor 61 of a hydrostatic continuously variable transmission 6 are configured as a variable displacement type. A hydraulic actuator 64 is provided to change a swash plate angle of the hydraulic motor 61. An operation circuit 65 for supplying a pilot pressure branched from a high pressure side oil passage 62H to the hydraulic actuator 64 is connected to the high pressure side oil passage 62H of a closed circuit 62 connecting the hydraulic pump 60 and the hydraulic motor 61. The operation circuit 65 is connected to a low speed operation side of the hydraulic actuator 64 so as to operate a swash plate 61b of the hydraulic motor 61 to a low speed side according to a pressure increase of the high pressure side oil passage 62H.SELECTED DRAWING: Figure 4【課題】静油圧式無段変速装置の大型化を避けながら、走行装置の増減速を草刈作業に適した速度や出力で操作性良く行えるようにして、草刈作業を能率良く行えるようにする。【解決手段】静油圧式無段変速装置６の油圧ポンプ６０と油圧モータ６１が可変容量型に構成され、油圧モータ６１の斜板角度を変更操作する油圧アクチュエータ６４が備えられ、油圧ポンプ６０と油圧モータ６１を接続する閉回路６２の高圧側油路６２Ｈに、その高圧側油路６２Ｈから分岐したパイロット圧を油圧アクチュエータ６４へ供給する操作回路６５が接続され、操作回路６５は、高圧側油路６２Ｈの圧力上昇に伴って油圧モータ６１の斜板６１ｂを低速側に操作するように、油圧アクチュエータ６４の低速操作側に接続されている。【選択図】図４
