Abstract: The sleep inducing device includes: an input receiving unit for receiving an input of a user; a background sound output unit for outputting a first signal corresponding to a background music having a melody and a rhythm according to the input of the user; a sleep inducing sound output unit for outputting a second signal having a maximum amplitude at a sleep inducing frequency and corresponding to a sleep inducing sound having a pitch varying to produce a consonance with the melody of the background music; and a mixing unit mixing the first signal and the second signal to output a mixing signal. The user can feel more comfortable while sleeping by changing the pitch of the sleep inducing sound to coincide with the melody of the background music.