An image display device displaying an image signal input from an external device and transmitting a control signal corresponding to a user input signal for controlling the external device to a relay device, the image display device comprising: an external device interface unit configured to connect the image display device with the external device; a display unit configured to display an image received from the external device; a user input interface unit configured to receive an input signal and to send a control signal corresponding to the input signal to the relay device acting as a communication relay between the image display device and the external device; and a controller configured to: in response to the image display device being powered on, check (S11, S12; S21, S22; S108) whether or not a connection log of the image display device includes a previous connection between the image display device and the relay device, scan (S14; S24) for an advertisement packet from the relay device at a first scan interval when the connection log does not include the previous connection between the image display device and the relay device, and scan (S13; S23; S109) for the advertisement packet from the relay device at a second scan interval having a longer time duration than the first scan interval when the connection log includes the previous connection between the image display device and the relay device. an external device interface unit configured to connect the image display device with the external device; a display unit configured to display an image received from the external device; a user input interface unit configured to receive an input signal and to send a control signal corresponding to the input signal to the relay device acting as a communication relay between the image display device and the external device; and a controller configured to: in response to the image display device being powered on, check (S11, S12; S21, S22; S108) whether or not a connection log of the image display device includes a previous connection between the image display device and the relay device, scan (S14; S24) for an advertisement packet from the relay device at a first scan interval when the connection log does not include the previous connection between the image display device and the relay device, and scan (S13; S23; S109) for the advertisement packet from the relay device at a second scan interval having a longer time duration than the first scan interval when the connection log includes the previous connection between the image display device and the relay device. in response to the image display device being powered on, check (S11, S12; S21, S22; S108) whether or not a connection log of the image display device includes a previous connection between the image display device and the relay device, scan (S14; S24) for an advertisement packet from the relay device at a first scan interval when the connection log does not include the previous connection between the image display device and the relay device, and scan (S13; S23; S109) for the advertisement packet from the relay device at a second scan interval having a longer time duration than the first scan interval when the connection log includes the previous connection between the image display device and the relay device.