A liquid treatment apparatus includes a liquid storing vessel, a first electrode, a second electrode at least partly arranged inside the vessel, a tubular first insulator surrounding a first-electrode lateral surface with a first space interposed therebetween, and including a first opening in an end surface in contact with the liquid, a tubular second insulator surrounding the first-electrode lateral surface inside the first insulator, a gas supply device supplying gas into the first space and ejecting the gas into the liquid through the first opening, and a power supply applying a voltage between the first and second electrodes and producing plasma. The second insulator is arranged with a second space interposed between the first and second insulators. Portions of the first and second insulators, those portions being positioned inside the vessel, are covered with the gas when the gas is supplied into the first space by the gas supply device.