Disclosed is an aeration device having doubled air intake force, given the same power, so as to take in water filling an inflow tube unit, through which air flows in, during an initial phase of startup, without using a separate means. The aeration device comprises: a hollow casing containing a motor; a mixing unit installed in front of the casing, the mixing unit having a discharge hole formed in the radial direction, a driving shaft of the motor extending through the mixing unit from the rear to the front; an impeller rotatably installed inside the mixing unit and fastened to the driving shaft to generate a flow in the radial direction of the mixing unit; an intake housing installed in front of the mixing unit, multiple intake holes being formed in the intake housing; and an air inflow unit extending through the intake housing from the front to the rear and having an extension tube unit extending towards the impeller, wherein the aeration device has an auxiliary intake unit extending forwards from the impeller to be inserted into the extension tube unit, the auxiliary intake unit rotating together with the impeller and providing a fluid inside the air inflow unit with intake force. Therefore, air intake force is doubled, given the same power, so as to take in water filling the inflow tube unit, through which air flows in, during an initial phase of startup, without using a separate means, thereby enabling efficient aeration even at a deep level.