An energy gathering device and an ultrasonic humidifier relate to a field of humidifier technology. The energy gathering device includes an energy gathering tube and an energy gathering floating body. The energy gathering device is arranged in a mist outlet tube. The mist outlet tube is disposed inside a water tank of an ultrasonic humidifier. The energy gathering floating body includes an energy gathering cavity. A first end of the energy gathering cavity is communicated with a second end of the energy gathering cavity. An extension direction of the energy gathering cavity is same as an extension direction of a tube cavity of the mist outlet tube. The energy gathering tube is fixed in the energy gathering cavity. A tube cavity of the energy gathering tube is communicated with the energy gathering cavity of the energy gathering floating body.