A light irradiation apparatus focuses light on a surface or an inside of an object to observe or process the object, and includes a laser light source, a lens, a lens, a mask, a wave plate, and a lens. The mask is a multi-ring mask for spatially intensity-modulating input light in a beam cross-section and outputting modulated light, and includes a plurality of ring-shaped light-shielding areas provided around a center position, and a transmitting area provided between two adjacent light-shielding areas out of the plurality of light-shielding areas. A radial width of each of the two adjacent light-shielding areas out of the plurality of light-shielding areas is larger than a radial width of the transmitting area provided between the two light-shielding areas.