In order to obtain a beam splitting prism which a beam can be split with simpler configuration in a state in which an optical path length is precisely controlled, there is provided a beam splitting prism having an incident and an outgoing faces orthogonal or parallel to each other, wherein transparent mediums, at least one beam splitter, and at least one reflector are combined so that the beam splitter and the reflector are located between the transparent mediums, the beam splitter and the reflector are arranged whose normal directions are orthogonal to each other, whereby a beam incident from an incident end face is outputted from an outgoing end face in the form of a plurality of split output beams.