An image forming apparatus comprising: a rotatable electrostatic latent image holder for holding electrostatic latent images on the circumferential face thereof, and a developing device, the developing device comprising: stirring members (72, 74) for stirring a developer-tank-contained developer containing toner and carrier inside a developer tank while conveying the developer along conveying passages (68, 70), a developer holder disposed adjacent to said stirring members (72, 74) to supply the stirred developer-tank-contained developer to an electrostatic latent image holder, a developer replenishing tank for replenishing the toner and the carrier to said developer tank, and a discharging mechanism for discharging an excessive amount of the developer-tank-contained developer outside said developer tank from a discharge opening section when the amount of the developer-tank-contained developer to be conveyed using said stirring members (72, 74) inside said developer tank exceeds a predetermined amount, characterised in that said stirring members (72, 74) comprise an upper stirring member and a lower stirring member disposed so as to be opposed to said upper stirring member, said conveying passages (68, 70) include an upper conveying passage in which said upper stirring member is disposed, a lower conveying passage in which said lower stirring member is disposed, a first communicating passage for connecting the downstream side of said upper conveying passage to the upstream side of said lower conveying passage and a second communicating passage for connecting the downstream side of said lower conveying passage to the upstream side of said upper conveying passage, and include a circulation passage through which the developer-tank-contained developer circulates using said upper conveying passage, said first communicating passage, said lower conveying passage and said second communicating passage, said discharging mechanism is disposed in the downstream end section of said upper conveying passage, and a bottom face on the downstream side of said upper conveying passage is positioned above a bottom face on the upstream side of said lower conveying passage, and said first communicating passage is disposed tilted downward in the gravitational direction at a tilt angle (β) with respect to a horizontal plane (xy). stirring members (72, 74) for stirring a developer-tank-contained developer containing toner and carrier inside a developer tank while conveying the developer along conveying passages (68, 70), a developer holder disposed adjacent to said stirring members (72, 74) to supply the stirred developer-tank-contained developer to an electrostatic latent image holder, a developer replenishing tank for replenishing the toner and the carrier to said developer tank, and a discharging mechanism for discharging an excessive amount of the developer-tank-contained developer outside said developer tank from a discharge opening section when the amount of the developer-tank-contained developer to be conveyed using said stirring members (72, 74) inside said developer tank exceeds a predetermined amount, characterised in that said stirring members (72, 74) comprise an upper stirring member and a lower stirring member disposed so as to be opposed to said upper stirring member, said conveying passages (68, 70) include an upper conveying passage in which said upper stirring member is disposed, a lower conveying passage in which said lower stirring member is disposed, a first communicating passage for connecting the downstream side of said upper conveying passage to the upstream side of said lower conveying passage and a second communicating passage for connecting the downstream side of said lower conveying passage to the upstream side of said upper conveying passage, and include a circulation passage through which the developer-tank-contained developer circulates using said upper conveying passage, said first communicating passage, said lower conveying passage and said second communicating passage, said discharging mechanism is disposed in the downstream end section of said upper conveying passage, and a bottom face on the downstream side of said upper conveying passage is positioned above a bottom face on the upstream side of said lower conveying passage, and said first communicating passage is disposed tilted downward in the gravitational direction at a tilt angle (β) with respect to a horizontal plane (xy).