A head-mountable information processing apparatus worn on a user's head and having a function for viewing images or hearing audio, the head-mountable information processing apparatus comprising: an audio input interface (132, 133, 601) worn in the vicinity of the user's ear, and being configured to collect ambient sound that occurs outside the head-mountable information processing apparatus and enters the ear, and convert the ambient sound into an input audio signal; an audio output interface (122, 602) configured to generate an output audio signal, convert the generated output audio signal into an audio for output, and emit the audio for output toward the user, and a controller configured to control an operation of the head-mountable information processing apparatus, wherein, based on a volume level of the input audio signal from the audio input interface and a volume level of the output audio signal from the audio output interface, the controller determines whether or not a state in which the ambient sound is preventing the audio for output from being heard is occurring, and based on a determination result, the controller controls a sound emission operation of the audio output interface, wherein, if it is determined that a state in which the ambient sound is not preventing the audio for output from being heard is occurring, the controller causes the audio output interface to perform sound emission, and if it is determined that the state in which the ambient sound is preventing the audio for output from being heard is occurring, the controller instructs the audio output interface to interrupt sound emission, and wherein the controller has: a threshold generator configured to generate a threshold level according to the volume level of the output audio signal; and a comparator configured to compare the volume level of the input audio signal and the threshold level to determine whether or not to instruct the audio output interface to interrupt sound emission. an audio input interface (132, 133, 601) worn in the vicinity of the user's ear, and being configured to collect ambient sound that occurs outside the head-mountable information processing apparatus and enters the ear, and convert the ambient sound into an input audio signal; an audio output interface (122, 602) configured to generate an output audio signal, convert the generated output audio signal into an audio for output, and emit the audio for output toward the user, and a controller configured to control an operation of the head-mountable information processing apparatus, wherein, based on a volume level of the input audio signal from the audio input interface and a volume level of the output audio signal from the audio output interface, the controller determines whether or not a state in which the ambient sound is preventing the audio for output from being heard is occurring, and based on a determination result, the controller controls a sound emission operation of the audio output interface, wherein, if it is determined that a state in which the ambient sound is not preventing the audio for output from being heard is occurring, the controller causes the audio output interface to perform sound emission, and if it is determined that the state in which the ambient sound is preventing the audio for output from being heard is occurring, the controller instructs the audio output interface to interrupt sound emission, and wherein the controller has: a threshold generator configured to generate a threshold level according to the volume level of the output audio signal; and a comparator configured to compare the volume level of the input audio signal and the threshold level to determine whether or not to instruct the audio output interface to interrupt sound emission. a threshold generator configured to generate a threshold level according to the volume level of the output audio signal; and a comparator configured to compare the volume level of the input audio signal and the threshold level to determine whether or not to instruct the audio output interface to interrupt sound emission.