A signal branching filter according to the invention is a signal branching filter connected to a network having at least four terminals. The signal branching filter includes a first line one end of which is connected to a first terminal of the network, a second line one end of which is connected to a second terminal of the network, a third line one end of which is connected to a third terminal of network, and a fourth line one end of which is connected to a fourth terminal of the network. The other end of the first line and the other end of the second line are connected to each other at a first node, and the other end of the third line and the other end of the fourth line are connected to each other at a second node. When a signal is received from the first node, a phase difference between a phase of a signal appearing on a second node side of the third line and a phase of a signal appearing on a second node side of the fourth line is almost 180°±360°*n is an integer equal to or larger than 0).