projected from the front and rear ends of the self propelled vehicle 1 for engagement with for example poles driven into the end area 27 of the culture ground and in the end of the valley 23 opposite to the end area 27 when the vehicle 1 runs in one and the other direction the switch bar 4 or 5 is pressed by the pole upon contact therewith so that a lever 4 39 or 5 39 of a forward backward change over limit switch ls f or ls b is activated to change the direction of operation of the electric motor m d whereby the switching of the running direction of the vehicle 1 is automatically effected to enable the vehicle 1 to reciprocatingly move along the valley 23 the self propelled vehicle 1 has a reversing limit switch ls r which has a resilient sensor rod 30 projected from the portion of the front end of the vehicle 1 adjacent to the switch bar 4 the sensor rod 30 ahead of the switch bar 4 when the carrier 7 carrying the self propelled vehicle 1 traverses along the rails 16 16 the sensor rod 30 engages with one of reversing poles 32 which are arranged at the same pitch as the ridges 22 in consequence the reversing limit switch ls r is activated to lower the self propelled vehicle onto the center of the next valley 23 in this case therefore the pole 32 driven into the end area 27 of the culture ground is located on the trailing side of the center.