An ultrasonic container sealing method of sealing a closure 12 to a container main body 11 with use of an ultrasonic horn 54 having a sealing action face 53 comprises applying pressure to a lap of an outer peripheral portion of the closure 12 and a flange 24 of the container main body 11 as lapped over each other by the sealing action face 53, and causing ultrasonic rotational vibration in a rotating direction about an axis parallel to the direction of application of the pressure to act on the sealing action face 53.