The purpose of the invention is to simplify the linkage mechanism of a shift operating device and to unitize the shift operating device so as to improve the reliability of assemble accuracy. A forward traveling pedal and a rearward traveling pedal are rotatably supported by a installation plate; the installation plate rotatably supports a shift operating rotary sleeve connected through one link to the basal end of the forward traveling pedal (a forward traveling pedal rotary sleeve) and connected through one link to the basal end of the rearward traveling pedal (a rearward traveling pedal rotary sleeve); the forward traveling pedal, the rearward traveling pedal, the shift operating rotary sleeve and the installation plate are constructed as an integral unit; and the shift operating rotary sleeve is rotated forward and rearward interlockingly with the operation of the forward traveling pedal and the rearward traveling pedal so as to slant swash plates of a hydraulic pump and a hydraulic motor of a HST.