PURPOSE:To facilitate confirmation and amendment of course, by providing a marker for confirming the advancing direction integrally with a base body for straight drive induction and preferentially carrying out a steering operation in carrying out the steering operation during driving by straight drive controlling device. CONSTITUTION:A center marker 57 and side marker 58 are attached on the upper face of a guide float 40 and a machine body is followed to the skid direction of the guide float which is a base body for inducing straight drive and straight drive running is maintained. An operator may sometimes only confirm the course from the visual relation between guide marker 58 in already planted side and seedling line planted in previous process during planting opera tion. When a steering handle 17 is operated, an operation detecting sensor is perceived and the guide float 40 is temporarily raised and amendment of advanc ing direction or running of curve part, etc., is carried out.
