Provided is a multi-mode resonator in which four resonance modes are degenerated, a dielectric member is not necessarily required, and enhanced efficient use of space is obtained. A multi-mode resonator 1 is a multi-mode resonator in which four resonance modes are degenerated, this resonator including an exterior conductor 2 made of a metal material, and formed in the shape of a box, wherein both ends of a cylindrical circumferential wall section 2c are closed off by a first end section 2a and a second end section 2b; a columnar first central conductor disposed inside the exterior conductor 2, one end 3a being shorted to the first end section 2a of the exterior conductor 2 and another end 3b being left open; and a columnar second central conductor disposed inside the exterior conductor 2, one end 4a being shorted to the second end section 2b of the exterior conductor 2 and another end 4b being left open.