A control device for a vehicle generator includes a shared terminal to be connected to a communication IF or a lamp IF via a switch; and a nonvolatile PROM which controls the switch based on shared terminal setting data and carries out switching between the IFs to be connected to the shared terminal. The PROM stores therein shared terminal setting data “communication IF effective” as its initial setting. The shared terminal setting data stored in the PROM can, when necessary, be rewritten into “lamp IF effective” via the shared terminal, the communication IF, and a memory controller.