A resonator 15 includes: a main shaft 12 that is coupled to an ultrasonic vibrator 11 and extends in an advancement direction of an ultrasonic wave generated from the ultrasonic vibrator 11; and protrusions 13a and 13b protruding in a direction intersecting a longitudinal direction from a center plane Lc in the longitudinal direction of the main shaft 11, wherein a plurality of holes 41a, 41b are formed symmetrically with respect to a central plane Lc in the longitudinal direction of the main shaft 12, inside a section substantially orthogonal to a protruding direction of the protrusions 13a and 13b in the vicinity of the center in the longitudinal direction of the main shaft 12 from which the protrusions 13a, 13b protrude.