An EUV light source is configured for generating an EUV light for an exposure device. The EUV light source includes a chamber, a target supply device configured for supplying a target into the chamber, an optical system for introducing laser light from a driver laser into the chamber and irradiating the target with the laser light to turn the target into plasma from which EUV light is emitted, and an EUV collector mirror in the chamber. The EUV collector mirror may include a multilayered reflecting surface with grooves and collect the EUV light from the plasma to a focal spot. The grooves can be arranged in a concentric fashion, and be configured for diffracting at least light at a wavelength which is the same as that of the laser light from the driver laser.