An in-vehicle system includes a zone control unit and lower-level control units. The zone control unit includes: a power supply control unit configured to control power supply to each of the lower-level control units; a communication control unit configured to control communication with each of the lower-level control units; and an abnormality detection unit configured to detect presence or absence of an abnormality in each of the lower-level control units. In a case in which an abnormality for two or more of elements including a power supply current value, a communication response time, and a MAC address is detected in at least one of the lower-level control units, the abnormality detection unit is configured to recognize that the at least one of the lower-level control units is an unauthorized device.