PURPOSE: To enhance aeration effect and also to prevent generation of vibration and noise by-providing a propeller water-jet machine under the water surface so that the distance between the tip of a propeller and the water surface is regulated to the specified distance when the tip of the propeller is positioned upside.

CONSTITUTION: A water-jet machine 1 is fitted to a fitting frame 4 so that the axial line is made nearly horizontal. It is set so that distance H between the tip of the propeller 6 thereof and the water surface 7 is regulated to 2-20cm when the tip of the propeller 6 is positioned upside. Pond water 8 rises above the water surface according to upward motion of the propeller 6. Pond water 8 in the water surface is pulled underwater according to downward motion of the propeller 6 and also even the atmosphere is incorporated underwater. Moreover water intermittently becomes a vortex and the atmosphere is diffused underwater and aeration action is positively performed. At this time, the water- jet machine 1 is smoothly operated without generation of noise based on the propeller 6 and without accompanying violent vibration.