A dissolving water making unit and a bubble generating unit are provided. The dissolving water making unit includes a gas dissolving device for dissolving gas in water. The bubble generating unit includes a bubble generating nozzle and a bubble generating cartridge. The dissolving water making unit sucks water from a water source, and sucks gas to make dissolving water from a mixed solution in which the water and the gas are mixed together. The dissolving water is obtained by dissolving the gas in the water. The bubble generating unit generates microbubbles from the dissolving water supplied from the dissolving water making unit. The gas dissolving device includes a closed vessel; an inflow port which is provided in the closed vessel, and which is provided for causing the mixed liquid sucked from the source to flow into the closed vessel; an exhaust valve which is provided in an upper portion of the closed vessel, and which is provided for exhausting excess gas from the mixed liquid; and an outflow port which is provided near a bottom portion of the closed vessel, and which is provided for causing the dissolving water to flow out from the closed vessel to the bubble generating unit. Between the inflow port and the outflow port, the closed vessel has a retention region in which the dissolving water flows slowly, in which air is dissolved in the dissolving water to substantial saturation, and in which the dissolving water hardly contains fine bubbles.