To provide an irradiation device whereby the action of light which is irradiated towards an eyeball makes it possible to prevent myopia or delay the progression of myopia. An irradiation device 10 having a light source 1 and an instrument 2 on which the light source 1 is mounted solves the abovementioned problem by being configured such that the light source 1 emits at least light of a wavelength within a range of 350 nm to 400 nm, and is arranged at a position for irradiating in an eyeball direction when the instrument 2 is worn and also arranged at a position 0 to 100 mm from the surface of the eyeball. Herein, the configuration can be such that the irradiance of the light of the wavelength within the range of 350 nm to 400 nm is 0.02 to 1.0 W/m2 at the eyeball surface when the instrument 2 is worn.
