A teeth whitening device (10) includes a generator (30) configured to generate a teeth whitening fluid that whitens teeth and humidified gas, a mouthpiece (100) configured to supply the teeth whitening fluid and the humidified gas, and a coupling part (20) that couples the generator (30) and the mouthpiece (100) with each other. The mouthpiece (100) includes a first supply port (103) through which the teeth whitening fluid is supplied, and a second supply port (104) through which the humidified gas is supplied, the second supply port (104) being separated from the first supply port (103). The mouthpiece (100) further includes a first supply passage (101) configured to guide the teeth whitening fluid to the first supply port (103), and a second supply passage (102) configured to guide the humidified gas to the second supply port (104), the second supply passage (102) being separated from the first supply passage (101).
