According to the configuration of the present power splitter, it is possible to reduce the characteristic impedance of a transmission line constituting a directional coupler by setting the impedance of a first terminal pair constituted of an input port 7a and a second output port 7d of a 6-dB branch-line-shaped directional coupler 7 to a value smaller than a reference impedance Z0 (50 Ω in general) and setting the impedance of a second terminal pair constituted of an isolation port 7b and a first output port 7c of the directional coupler 7 to Z0. Therefore, it is possible to increase the number of split s and reduce loss, as compared with conventional cases.