An operating system for a tractor to which an implement is attachable, the operating system comprises: a steering wheel provided rearwardly of a hood that houses an engine located in a forward region of the tractor; a control panel provided rearwardly of the hood and adjacent the steering wheel; a center cover extending generally vertically below the steering wheel; an operation lever provided at a position laterally of the control panel; a valve unit with a pair of spools, the valve unit being located at a lower position with respect to the steering wheel and being covered by the center cover; a link mechanism that links the operation lever and the pair of spools, the link mechanism being covered by the center cover.