PROBLEM TO BE SOLVED: To provide a technology for simplifying a device configuration while securing the safety of illumination light in a device having a mechanism for irradiating light to a subject.SOLUTION: A light irradiation device includes: a probe including an emission part for guiding light from a light source to a subject, a housing including the emission part, and a touch sensor for acquiring a contact state quantity between the subject and the housing and a control device for controlling the irradiation of the light from the emission part on the basis of the degree of the contact state quantity and a change in the contact state quantity. The control device performs control that enables irradiation of light from the emission part when the contact state quantity is equal to or more than a first reference value and when a change in the contact state quantity is equal to or more than a second reference value in the case that a change in the contact state quantity is positive when the housing is pressed against the subject.
