A self-adaptive surge-proof circuit is used in a switching power supply device. The seat back includes a front support surface for supporting the seat occupant in an upright seating position. In addition, the coupling mechanism limits a movable direction of the support portion such that at least when the load applied to the leg increases, a direction of the relative positional displacement between the foot position and the position of center of gravity is substantially limited to a direction of flexion and extension of knee joint. A steering direction detector is provided to determine the direction of the steered wheel so that if the steered wheel is not directed substantially straight ahead, then operation of the truck from the supplemental controls is disabled. A virtual storage space is defined and established with a defined correspondence to the address space of the storage network.