To provide a covering member capable of covering a liquid level with no gap left.

The covering member 60 includes; a deformable outer shell member having a hollow part therein; and a filler member packed inside the outer shell member. The apparent specific gravity of the outer shell member and the filler member is smaller than that of the developer stored in a replenishing tank, and larger than that of the external air. When a plurality of covering members 60 are floated on the liquid level of the developer in the replenishing tank, the outer shell members of the covering members 60 are deformed to a nearly equilateral hexagon in a plane view so as to fill up the gaps formed between the covering members 60.