Provided is a bubble generating mechanism that does not use a complicated air mixing mechanism and generates micro-bubbles in a sufficient quantity. A flow path (2) that connects an inflow opening (2n) that opens on an inflow end and an outflow opening (2x) that opens on an outflow end is formed in a state passing completely through a member main body (6), and a constricted part (2c) the flow-through cross-sectional area of which is smaller than the inflow opening (2n) is formed in a position within that flow path (2). Colliding parts (3) that further reduce the cross-sectional area of the flow path in the constricted part (2c) are disposed in the constricted part (2c) in a state that divides the axial plane of the flow path (2) into three or more segment areas (2e).