Vehicle Communication Control Device

A vehicle communication control device for which an isolation boundary equipped with a signal isolation means is configured between (a) a microcomputer which is disposed in a high-voltage region supplied with a relatively high voltage and which controls an operation control signal sent to an operation control device for an electric equipment mounted on a vehicle that is provided in said high-voltage region and (b) a signal transmission/reception means which is disposed in a low-voltage region supplied with a relatively low voltage and which receives a control signal sent from a host controller, sends the received control signal toward said microcomputer, receives a signal sent from said microcomputer side, and sends the received signal toward said host controller side, wherein said signal isolation means is provided with a voltage monitoring means for monitoring a variation of voltage in a high-voltage side and/or a low-voltage side of said signal isolation means, and an erroneous output prevention means capable of controlling an output, which is from said signal isolation means to said high-voltage side and/or said low-voltage side of said signal isolation means, to a predetermined safe output or an output within a predetermined safety range when a voltage detected by said voltage monitoring means with respect to variation is reduced down to a value out of a predetermined range.