A circuit device includes a first physical layer circuit to which a first bus with a USB standard is coupled, a second physical layer circuit to which a second bus with the USB standard is coupled, and a bus monitor circuit monitoring the first bus and the second bus, in which the first physical layer circuit includes a first disconnect detection circuit which detects device disconnect in the first bus, the bus monitor circuit includes a first test signal detection circuit which detects whether or not a test signal is output to the first bus, and when detection of the device disconnect by the first disconnect detection circuit is disabled, detection of the test signal by the first test signal detection circuit is disabled.