An optical hair growth modulation device modulates hair growth by irradiating modulating light to skin. This device is provided with a modulating light irradiator for irradiating modulating light, a measuring light irradiator for irradiating measuring light for measurement of a target site of the human body to the target site, a light receiver for receiving the measuring light reflected from the target site, a processor for processing information of the measuring light received by the light receiver, and an irradiation determinator for judging whether or not to make the light irradiation from the modulating light irradiator based on a processing result of the processor. The irradiation determinator is configured to control irradiation of modulating light from the modulating light irradiator based on the judgment thereof. This device is able to judge whether or not a target site is suitable as a site to be irradiated with modulating light by using measuring light, thereby preventing an unsuitable site such as an eye ball from being accidentally irradiated with the modulating light.
