While one beam is being branched into a plurality of beams with different optical path lengths, the beams can be converged on the same position in the optical-axis direction with a simple structure even when relative angles between the beams differ. Provided is a beam splitter apparatus including a beam splitter that branches an input pulsed beam into two optical paths with different optical path lengths relay optical systems that are disposed in the respective branching optical paths and that relay pupils in the optical paths a beam splitter that multiplexes the relayed pulsed beams in the two optical paths and a reflection optical system that endows pulsed beams branching off via the beam splitter with a relative angle.
