A developing device includes a development casing, a developer carrying member, and a regulating blade. The development casing has an opening part. The developer carrying member has a developing area. The development casing has a blade facing part. The regulating blade includes a fixed part and a regulating part, and a space between the regulating part and the blade facing part is larger than a space between the fixed part and the blade facing part. The developing device further includes a blade seal member. The blade seal member is disposed between the regulating blade and the blade facing part, and is glued to an upstream side surface of the regulating part in the rotation direction, so as to seal a gap between the regulating blade and the blade facing part.