An object of the present invention is to provide a control unit for vehicle where increase in number of input/output and upgrading of function can easily be performed and, in addition to this, changing of a program in a control unit can easily be performed even when a single-chip micro-computer is used.In order to cope with an increase in input/output points and addition of function, a control unit is constructed such as to comprise interface software memory means storing an interface software program for connecting an application software program with an OS (operating system) in an internal ROM, a CPU (central processing unity for performing computation of the application software program and the interface software program, a RAM (erasable memory) storing data such as the result of computation, an I/O unit for extending the control unit, and extending means for communicating memory data through a bus or a LAN.A single-chip micro-computer used in vehicle control can easily cope with increase in input/output points or addition of function, and an application software program can continuously be used only by rewriting an interface software program, and further re-manufacturing of a core unit is unnecessary. Therefore, development of a control unit including programs becomes easy.