In an instantaneous wire interruption detection system for a vehicle electrical system, a VSC-ECU includes an input processing circuit that processes electric signals transmitted from various sensors and an EFI-ECU by a signal wire (wire harness); a signal state determination circuit that determines whether the electric signals processed by the input processing circuit are normal or abnormal; a latch circuit that latches the determination result as a latch signal; and an output circuit that can output the latch signal. When a signal abnormality is detected by the signal state determination circuit, the latch circuit is able to generate the latch signal in synchronization therewith, and latch the latch signal for a predetermined time. Accordingly, for example, by connecting a tester device to the output circuit, and monitoring the latch signal, it is possible to detect instantaneous wire interruption of the electrical system.