A plasma generator 1 includes a first electrode 12 provided in a gas storage section 5, and a second electrode 13 provided in such a manner that at least a portion coupled with the first electrode 12 comes into contact with a liquid 17 in a liquid storage section 4. Electrical discharge is caused between the first electrode 12 and the second electrode 13 so that plasma is produced in a gas region in the liquid 17 in the liquid storage section 4, and hydroxyl radical is produced from water contained in the liquid 17 and oxygen contained in the gas.
