Abstract: A disclosed battery supply control unit comprises a large current relay in which an excitation current continuously flows when it is in its connecting state and a small current relay in which a limited excitation current flows only at the time of changeover between its connecting state and non-connecting state. If loads require a large current, the large current relay and small current relay are maintained in the connecting state, and if the loads do not require the large current, the large current relay is maintained in the non-connecting state while the small current relay is maintained in the connecting state at least in a predetermined time.