To solve a problem in a connection state of an external device as a host with a USB wherein when something is abnormal in the external device of the host, the USB device continuously waits for transaction from the external device to into an incommunicable state, and it is required to pull out a USB cable, disconnect the USB connection, and insert the USB cable again for the connection.

This USB device 1 is provided with a circuit abnormality detector 2 detecting the abnormal state of the external device 5 according to the communication state of the external device 5 to be the host and a circuit control device 4 disconnecting and connecting the USB connection. This device is characterized in that, when the circuit abnormality detector 2 detects that something is abnormal in the external device 5, the circuit control device 4 once disconnects the USB connection and reconnects it so as to restore the incommunicable state of the USB connection.