A developing device includes: a developing tank for storing a developer containing a toner and a magnetic carrier, the developing tank including, inside thereof, a first developer carrying path; and a first stirring carrying member that rotates so that the first stirring carrying member carries the developer included in the first developer carrying path while stirring the developer. A toner supply opening is formed in a developing tank cover. An upper part of an inner wall surface of a side in which a developer sinks which inner wall surface faces downward rotation of the first stirring carrying member inclines from a direction perpendicular to a horizontal surface toward the first developer carrying path. An angle α made by (i) a tangential line of the upper inner wall surface at a position of the upper inner wall surface which position is at a height of a top part of an outer circumference of the first stirring carrying member and (ii) a horizontal line is not less than 100° but not more than 150°. This makes it possible to properly stir a supplied toner with an existing developer without applying excessive stress on the developer.