To provide a fine bubble generator capable of generating fine bubbles extremely small in bubble diameters with a small output pump.

The fine bubble generator 10 includes a pump 4 having a liquid sucking part sucking a liquid and a liquid discharging part discharging a liquid. A pipe 2 for circulation in the upstream of the pump 4 is attached with a bubble mixing-in part 3 sucking gas from the outside and mixing the gas into a liquid, The mixed-in gas is broken in the pump 4 and made to be fine bubbles. An embodiment of the bubble mixing part 3 may be a unit installed in the pump, may be a unit mixing gas into a liquid as swirl flow, a unit mixing gas into a liquid by using the Venturi effect, a unit having an orifice, and a unit mixing gas by pressuring from the outside.