Sound Output Device and Sound Output Method

The present invention notifies a listener that a target acoustic characteristic is not imparted to an acoustic output device worn by the listener. The sound output device includes a first imparter that imparts first sound characteristics to an input signal; a loudspeaker that outputs a sound based on a signal obtained by impartation of the first sound characteristics to the input signal; a first microphone that receives a sound based on the sound output by the loudspeaker; a determiner that obtains difference characteristics between frequency characteristics of the input signal and frequency characteristics of a signal derived from the sound received by the first microphone, to determine whether the difference characteristics fall within a predetermined range from target sound characteristics; and an instruction indicator that outputs an instruction for output of an alert if a result of the determination by the determiner is negative, and the first imparter corrects the first sound characteristics based on th