A vehicle-mounted gateway apparatus according to an embodiment includes a communication device including an external communication interface for connection to the network outside the mobile body with each of a plurality of different external communication schemes and an internal communication interface for connection to each of the plurality of data sources within the mobile body; and a control device configured to transmit data collected from each of the data sources through the internal communication interface to the network outside the mobile body. The control device includes a communication channel selection section configured to select a communication channel from the plurality of external communication schemes for each of the data sources, and a monitoring control section configured to monitor data output from each of the data sources and to transmit the data to the network outside the mobile body over a selected one of the communication channels associated with the data source. The communication channel selection section is configured to switch between the communication channels associated with each of the data sources depending on a communication connection state of each of the plurality of external communication schemes based on priority setting in which the plurality of external communication schemes are arranged in a predetermined priority order.