A light source apparatus has a luminescent tube, a reflecting mirror, a securing member and bonding material as a holding member disposed to block a part of a small opening of the reflecting mirror and holding the luminescent tube in the reflecting mirror, a transparent protection plate for blocking the large opening of the reflecting mirror, a ventilator for sucking air inside the reflecting mirror through the small opening and sending out the air through an outlet, and a housing for combining the reflecting mirror and the ventilator; and the reflecting mirror includes an air inlet disposed closer to the large opening than a center position of the luminescent tube.