To provide a microbubble generating mechanism allowing liquid to contain desired microbubbles.

The microbubble generating mechanism includes a gas-liquid mixing passage 11 mixing a liquid L and a gas G; a liquid introducing passage 13 introducing the liquid L to the gas-liquid mixing passage 11; a gas-liquid mixture lead-out passage 15 leading out a gas-liquid mixture M from the gas-liquid mixing passage 11; a gas introducing passage 17 introducing the gas G to the gas-liquid mixing passage 11; and a flow rate and bubble diameter regulating member 21 provided downstream of the gas-liquid mixing passage 11 to regulate the flow rate of the gas-liquid mixture M and the diameter of bubbles in the gas-liquid mixture M. The liquid introducing passage 13 is formed to be gradually reduced in cross-sectional area toward the gas-liquid mixing passage 11.