A head mounted display, HMD, comprising: a processor configured to control operation of the HMD; an audio output unit configured to output audio according to a command of the processor, wherein the audio output unit includes a left channel output unit and a right channel output unit; a sensor unit configured to detect at least one external digital device connected to the HMD and for transmitting whether at least one external digital device is connected to the HMD to the processor; and a communication unit configured to transmit/receive data to/from the external digital device according to a command of the processor, wherein the processor is further configured to receive an audio signal of the external digital device, to determine whether the received audio signal is directional output signal, to detect location information of the external digital device corresponding to the audio signal when the received audio signal is directional output signal, wherein the location information represents a relative location of the external digital device with respect to the HMD, to detect a location state of the external digital device based on the location information, wherein the location state includes a first state in which the external digital device is located within a predetermined view angle of the HMD and a second state in which the external digital device is not located within the view angle of the HMD, and to output the audio signal based on the detected location information and location state of the external digital device, wherein the audio signal output includes a left channel output and a right channel output, wherein at least one of the left channel output and the right channel output is controlled respectively based on the location information and the location state of the external digital device for outputting directional audio sound, appearing to a listener as if output from the direction in which the external digital device corresponding to the audio signal is located, wherein the processor is adapted to control an output level of the audio signal to be less or equal to predetermined level or blocks output of the audio signal when the location state of the external digital device corresponds to the second state and when a respective user input is received. a processor configured to control operation of the HMD; an audio output unit configured to output audio according to a command of the processor, wherein the audio output unit includes a left channel output unit and a right channel output unit; a sensor unit configured to detect at least one external digital device connected to the HMD and for transmitting whether at least one external digital device is connected to the HMD to the processor; and a communication unit configured to transmit/receive data to/from the external digital device according to a command of the processor, wherein the processor is further configured to receive an audio signal of the external digital device, to determine whether the received audio signal is directional output signal, to detect location information of the external digital device corresponding to the audio signal when the received audio signal is directional output signal, wherein the location information represents a relative location of the external digital device with respect to the HMD, to detect a location state of the external digital device based on the location information, wherein the location state includes a first state in which the external digital device is located within a predetermined view angle of the HMD and a second state in which the external digital device is not located within the view angle of the HMD, and to output the audio signal based on the detected location information and location state of the external digital device, wherein the audio signal output includes a left channel output and a right channel output, wherein at least one of the left channel output and the right channel output is controlled respectively based on the location information and the location state of the external digital device for outputting directional audio sound, appearing to a listener as if output from the direction in which the external digital device corresponding to the audio signal is located, wherein the processor is adapted to control an output level of the audio signal to be less or equal to predetermined level or blocks output of the audio signal when the location state of the external digital device corresponds to the second state and when a respective user input is received.