A phase shifter includes dielectric members including facing portions facing a signal line formed on a surface of a substrate and being made of a dielectric material, a supporting member configured to support the dielectric members and receive a moving force for moving the dielectric members in a direction which is parallel to the substrate and crosses the signal line, and a moving mechanism configured to apply the moving force to the supporting member. At least either the dielectric members or the supporting member is provided with a protrusion configured to keep a distance between the facing portions of the dielectric members and the signal line.