The present invention relates an aeration device including: a hollow casing having a motor mounted therein; a mixing unit formed on the front side of the casing and having a discharge hole formed in a radial direction and an intake hole formed on the front thereof; an impeller located inside the mixing unit and coupled to a driving shaft of the motor, the driving shaft being extended to the mixing unit, in such a manner as to be rotated unitarily with the driving shaft, to generate a flow in an outward radial direction upon the rotation; an air inflow unit having one side end portion located in front of the impeller and serving as an air inflow pipe for introducing air to the mixing unit; and an auxiliary intake unit located on the front side of the impeller in such a manner as to be rotated unitarily with the driving shaft of the motor and adapted to be inserted into the air inflow unit in such a manner as to allow s fluid in the air inflow unit to flow backward upon the rotation. Accordingly, the aeration device can improve the air intake force so as to suck the water filled in the inflow pipe introducing air at the beginning of starting, thus performing the aeration efficiently even in deep water.