A developing device has a developer tank for containing a two-component developer; a partition; a first and a second developer conveyance path for conveying the developer in pairs; a first conveyance member for conveying the developer in one direction, which has a first rotation axis, a first helical blade fixed to the first rotation axis, and a first passive gear provided to an end of the first rotation axis; a second conveyance member for conveying the developer in one direction, which has a second rotation axis, a second helical blade fixed to the second rotation axis, and a second passive gear provided to an end of the second rotation axis; a first communicating path; a second communicating path; a developing roller; and a rotation axis bending prevention belt provided so as to bridge the first and the second rotation axis outside the developer tank.