The present invention relates to an oxygen supply device for water quality improvement, comprising: a housing (15) configured such that water is introduced through an inlet (12) and discharged through an outlet; a bubble generating portion (10) comprising a Venturi tube portion (30) coupled to the outlet of the housing (15) such that water is introduced through the housing by a pressure difference between the outside and the interior of a channel resulting from a flow of compressed air supplied, through a supply tube (11), to a channel part having a reduced channel diameter, the bubble generating portion (10) thereby mixing the introduced water and the flow of compressed air such that bubbles are generated and discharged; a moving means (40) for moving the bubble generating portion (10) in the upward/downward direction while supporting the same; and a frame (50) for supporting the moving means (40) while being partially submerged in seawater. The present invention is advantageous in that the upward/downward p
