To provide an irradiation device capable of preventing myopia or slowing the progression of myopia by the action of light irradiated toward the eyeball. An irradiation device (10) comprises a light source (1) and an instrument (2) on which the light source (1) is mounted. The light source (1) emits at least light having a wavelength within a range of 350 to 400 nm, inclusive, and is disposed in a position that allows irradiation in an eyeball direction when the instrument (2) is mounted. Further, the light source (1) is disposed in a position 0 to 100 mm, inclusive, from a surface of the eyeball. At this time, an irradiance of the light having a wavelength within the range of 350 to 400 nm, inclusive, is 0.02 to 1.0 W/m2, inclusive, on the eyeball surface when the instrument (2) is worn.
