A sound output device is configured to be installed in a vehicle. The sound output device includes a driving-status detector for detecting a driving status of the vehicle, a sound signal generator for generating a reference signal in response to the detected driving status, first and second units for processing the generated reference signal, first and second sound output parts for outputting the reference signals processed by the first and second units. The first unit includes a phase shifter for shifting a phase of the reference signal such that the reference signals output from the first sound output part and the second sound output part have a phase difference between the respective reference signals. This sound output device allows a passenger at a predetermined position to hear the sound in a preferable condition.