PURPOSE: To prevent the occurrence of malfunction or the like by extending a vertically operating member from the side of a liftable seat, fixing a seating detection switch in an approximately horizontal direction faced to the aforesaid operating member, and keeping the slide stroke of a switch operation slide lever constant, regardless of a change in the weight of an operator.

CONSTITUTION: A tractor has a seat 6 placed on a hydraulic case 12 installed on top of a transmission case via a shock absorbing device 23. In this case, a switch bracket 11 is fixed to a bracket 19 projected for supporting the shock absorbing device 23 from a rear seat support seat 15 fixed on the hydraulic case 12, using a longitudinally adjusting bolt 18, and a seating detection switch 5 and an intermediate member 2 are fitted to the bracket 11. In addition, a vertically operating member 1 is fixed to the lower side of the seat 6 for the operation of the seating detection switch 5 via the intermediate member 2. The end of a switch operation slide lever 4 for the seating detection switch 5 is provided with a contact head 3, and an inclined contact section 1a at the lower end of the vertically operating member 1 is kept free to contact the tip of the aforesaid contact head 3.