A water saving aerator adapted to be attached to a water tap for generating bubble foam water and flowing the bubble foam water, comprising; a water flow forming portion for forming a water flow through the water saving aerator; a water flow accelerator for accelerating the water flow supplied from the water flow forming portion by narrowing its width and jetting an accelerated water flow jet downward; an inner cylindrical pipe provided with an air intake hole; and an outer cylindrical pipe enclosing the inner cylindrical pipe, the outer cylindrical pipe being arranged below the water flow forming portion; wherein a space between the inner cylindrical pipe and the outer cylindrical pipe constitutes a water flow cylinder through which the water accelerated by the water flow accelerator flows; wherein the water flow accelerator is configured to flow the accelerated water flow jet obliquely downward to hit an outer cylindrical surface of the water flow cylinder and to reflect the water flow jet obliquely downward for diffusing the width of the accelerated water jet to cover the width of the water flow cylinder; wherein the air intake hole is provided in the inner cylindrical pipe below and adjacent the water flow forming portion; wherein an air cavity is provided in an inner space of the water flow cylinder, wherein the air cavity is always filled with air even when water flushes into it; wherein a width of the accelerated water flow jet is narrower than that of the water flow cylinder; wherein a ventilation pass for supplying outer air to the air cavity via the air intake hole is provided inside the inner cylindrical pipe; and wherein the accelerated water flow jet accelerated by the water flow accelerator is jetted into the air contained in the air cavity supplied from the air intake hole, the bubble foam water flow is generated by injecting the air from the air intake hole into the water flow with the force generated by the air pressure decrease by the accelerated water flow jet. a water flow forming portion for forming a water flow through the water saving aerator; a water flow accelerator for accelerating the water flow supplied from the water flow forming portion by narrowing its width and jetting an accelerated water flow jet downward; an inner cylindrical pipe provided with an air intake hole; and an outer cylindrical pipe enclosing the inner cylindrical pipe, the outer cylindrical pipe being arranged below the water flow forming portion; wherein a space between the inner cylindrical pipe and the outer cylindrical pipe constitutes a water flow cylinder through which the water accelerated by the water flow accelerator flows; wherein the water flow accelerator is configured to flow the accelerated water flow jet obliquely downward to hit an outer cylindrical surface of the water flow cylinder and to reflect the water flow jet obliquely downward for diffusing the width of the accelerated water jet to cover the width of the water flow cylinder; wherein the air intake hole is provided in the inner cylindrical pipe below and adjacent the water flow forming portion; wherein an air cavity is provided in an inner space of the water flow cylinder, wherein the air cavity is always filled with air even when water flushes into it; wherein a width of the accelerated water flow jet is narrower than that of the water flow cylinder; wherein a ventilation pass for supplying outer air to the air cavity via the air intake hole is provided inside the inner cylindrical pipe; and wherein the accelerated water flow jet accelerated by the water flow accelerator is jetted into the air contained in the air cavity supplied from the air intake hole, the bubble foam water flow is generated by injecting the air from the air intake hole into the water flow with the force generated by the air pressure decrease by the accelerated water flow jet.