A teeth whitening device includes a generator configured to generate a teeth whitening fluid that whitens teeth and humidified gas, a mouthpiece configured to supply the teeth whitening fluid and the humidified gas, and a coupling part that couples the generator and the mouthpiece with each other. The mouthpiece includes a first supply port through which the teeth whitening fluid is supplied, and a second supply port through which the humidified gas is supplied, the second supply port being separated from the first supply port. The mouthpiece further includes a first supply passage configured to guide the teeth whitening fluid to the first supply port, and a second supply passage configured to guide the humidified gas to the second supply port, the second supply passage being separated from the first supply passage.
