The plasma-generating apparatus includes a treatment vessel 509 containing to-be-treated water 510, a first electrode 504 and a second electrode 502 within the treatment vessel, a bubble-generating part which generate a bubble 506 such that a surface where conductor of the first electrode 504 is exposed to the to-be-treated water is positioned within the bubble 506, a gas-supplying apparatus 505 which supplies gas to the bubble-generating part, a pulsed power supply 501 connected to the first and the second electrodes 502 and 504, a control apparatus 520 which controls one or both of the gas-supplying apparatus and the power supply such that the voltage is applied between the first and the second electrodes 502 and 504 when at least surface where the conductor of the first electrode 504 is exposed is positioned within the bubble.