A light irradiating apparatus that may include: an ultraviolet light emission lamp configured to emit vacuum ultraviolet light toward a workpiece to be disposed in an atmosphere of a treatment gas including oxygen; a light passing window adapted to be disposed between the workpiece and the ultraviolet light emission lamp and configured to allow the vacuum ultraviolet light from the ultraviolet light emission lamp to pass therethrough, in which the light passing window has a light-exiting surface; and a spacer adapted to be disposed between the light passing window and the workpiece, to apply a pressing force onto the workpiece and to form a gap that allows a distance from the light-exiting surface of the light passing window to a surface of the workpiece to be of a uniform size over the entire surface of the workpiece.