A developing device includes a developing tank having a developing region tank and an agitating region tank, a partition wall member, a first agitating and conveying member, a second agitating and conveying member, a first intermediate wall member, a second intermediate wall member and a sensor, and an opening portion is formed. In the developing device, a third agitating and conveying member extending in a longitudinal direction of the agitating region tank is provided between the second agitating and conveying member and the second intermediate wall member in a transverse direction of the agitating region tank.