A sound output device of the present invention for outputting sound according to audio data fed thereto includes: a volume adjuster that is operated by a user in a predetermined manner, and that determines a ratio of volume of the sound to predetermined reference volume according to how it is operated by the user; a time detector detecting that a predetermined time has come; and a reference volume adjuster adjusting the reference volume according to a detection result of the time detector. Thus, the maximum level of the volume (which is dependent on the reference volume) can be automatically adjusted according to the current time. The volume adjuster determines the ratio of volume to reference volume according to the operation by the user. Thus, for example, the same operation performed by the user even under different levels of reference volume produces almost the same ratio of volume to reference volume. As a result, ease with which the user adjusts the volume can be prevented as much as possible from being impaired.