A laser system capable of appropriately controlling the energy of a laser beam pulse is provided. An exemplary laser system of the present disclosure may control an optical isolator to switch from a closed state to an open state and then to return to the closed state for each of the laser beam pulses repeatedly outputted from a master oscillator. The laser system may control the optical attenuator to set an optical transmittance of the optical attenuator for each of the laser beam pulses repeatedly outputted from the master oscillator.