An integrated circuit device includes a high-speed serial interface circuit that includes a receiver circuit that receives differential signals through a serial bus, first and second guard terminals that prevent radiation, first and second terminals that are disposed between the first and second guard terminals and receive the differential signals, a first power supply terminal to which a high-voltage-side power supply voltage for the receiver circuit is supplied, and a second power supply terminal to which a low-voltage-side power supply voltage is supplied. A first switch element is provided between a line from the first guard terminal and a line from the second power supply terminal, and a second switch element is provided between a line from the second guard terminal and a line from the second power supply terminal. The first and second switch elements are turned ON in a high-speed serial interface mode.