According to one embodiment, an external device includes a switching module configured to switch an external display, which is to be connected to a port of a display control circuit in an information processing device, between first and second external displays connected to the external device. A controller detects a state of a first detection signal representing whether or not a first external display is connected to the external device and a state of a second detection signal representing whether or not a second external display is connected to the external device. The controller controls the switching module based on the detected states of the first and second detection signals and a display priority.