1. A beam delivery system configured to deliver a pulse laser beam outputted from a laser apparatus to a target in an extreme ultraviolet light generation apparatus configured to generate extreme ultraviolet light by irradiating the target with the pulse laser beam, the beam delivery system comprising:a plurality of beam adjusters configured to adjust a divergence angle of a pulse laser beam outputted from the laser apparatus;
a beam sampler configured to separate a part of the pulse laser beam outputted from a first beam adjuster provided at the most downstream among the plurality of beam adjusters to acquire a sample beam;
a beam monitor configured to receive the sample beam and output a monitored diameter; and
a beam delivery controller configured to control the plurality of beam adjusters based on the monitored diameter,
wherein the beam delivery controller is configured to:
adjust each of beam adjusters other than the first beam adjuster selected one after another from the most upstream so that the monitored diameter at the beam monitor becomes a predetermined value specific to the beam adjuster; and
adjust the first beam adjuster so that the pulse laser beam becomes focused at a position downstream of a target position, and
wherein the first beam adjuster is a final-stage beam adjuster in the beam delivery system.