There is provided a laser unit that may include a master oscillator, a laser amplifier, and an adjuster. The master oscillator may be configured to output a laser light beam. The laser amplifier may be disposed in a light path of the laser light beam outputted from the master oscillator. The adjuster may be disposed in the light path of the laser light beam, and may be configured to adjust a beam cross-sectional shape of the laser light beam amplified by the laser amplifier to be a substantially circular shape. The beam cross-sectional shape may be at a beam waist of the laser light beam or in the vicinity of the beam waist of the laser light beam, and may be in a plane orthogonal to a light path axis.