A liquid treatment apparatus comprising: a dielectric tube through which water to be treated flows; a first electrode at least a part of which is disposed in the dielectric tube ; a second electrode at least a part of which is disposed in the dielectric tube , characterized in that the second electrode is at a position upstream of the first electrode such that the water to be treated flows from the second electrode toward the first electrode ; a gas supplier is configured to supply a gas for generating a bubble that covers a conductor-exposed portion of the first electrode ; and a power supply configured to apply a voltage between the first electrode and the second electrode in a state in which the conductor-exposed portion of the first electrode is covered by the bubble , wherein a longitudinal direction of the first electrode crosses a direction in which the water to be treated flows from the second electrode toward the first electrode in the dielectric tube , the liquid treatment apparatus further comprising: an insulator disposed in the dielectric tube so as to form a space around the first electrode , the insulator having an opening through which the space is connected to the dielectric tube , wherein the gas supplier is configured to generate the bubble in the water to be treated from the opening in the insulator by supplying the gas to the space , and the power supply is configured to cause an electrical discharge in the bubble and generates plasma by applying the voltage between the first electrode and the second electrode . a dielectric tube through which water to be treated flows; a first electrode at least a part of which is disposed in the dielectric tube ; a second electrode at least a part of which is disposed in the dielectric tube , characterized in that the second electrode is at a position upstream of the first electrode such that the water to be treated flows from the second electrode toward the first electrode ; a gas supplier is configured to supply a gas for generating a bubble that covers a conductor-exposed portion of the first electrode ; and a power supply configured to apply a voltage between the first electrode and the second electrode in a state in which the conductor-exposed portion of the first electrode is covered by the bubble , wherein a longitudinal direction of the first electrode crosses a direction in which the water to be treated flows from the second electrode toward the first electrode in the dielectric tube , the liquid treatment apparatus further comprising: an insulator disposed in the dielectric tube so as to form a space around the first electrode , the insulator having an opening through which the space is connected to the dielectric tube , wherein the gas supplier is configured to generate the bubble in the water to be treated from the opening in the insulator by supplying the gas to the space , and the power supply is configured to cause an electrical discharge in the bubble and generates plasma by applying the voltage between the first electrode and the second electrode . an insulator disposed in the dielectric tube so as to form a space around the first electrode , the insulator having an opening through which the space is connected to the dielectric tube , wherein the gas supplier is configured to generate the bubble in the water to be treated from the opening in the insulator by supplying the gas to the space , and the power supply is configured to cause an electrical discharge in the bubble and generates plasma by applying the voltage between the first electrode and the second electrode . <EOS>