A liquid treatment device comprises: a first insulator including a first opening and a first inner surface, a gas being emitted into a subject liquid through the first opening; a first electrode that is at least partially disposed within a first space surrounded by the first inner surface; a second electrode that is at least partially disposed within the subject liquid; a gas supply source; and a power supply source. The first inner surface includes a first partial region which contacts the first opening. A forward end of the first electrode protrudes from the first opening to outside the first space, or the forward end retreats from the first opening into the first space by less than 3 mm. A first distance, which is a shortest distance between an outer surface of the first electrode and the first partial region, is 1 mm or greater.