Information on a use situation of a portable electronic apparatus possessed by a user is acquired from an illuminance sensor, a contact sensor, and a GPS portion as use situation-acquiring portions, and a volume of a sound outputted either to a speaker provided as an internal sound-outputting unit in the portable electronic apparatus or to an external sound-outputting unit such as a headphone is controlled in accordance with the acquired information. Thus, even when a plug of the headphone falls off from the portable electronic apparatus despite an intention of the user, an unpleasant sound is prevented from being outputted from the speaker to a circumference.