A developing unit includes: a developing roller; a first conveying member provided in a first container, having a first shaft and a spiral blade, that agitates and conveys developer; a second conveying member provided in a second container connected to the first container via a hole, having a second shaft and a spiral blade, that agitates and conveys the developer; and a supplying member having a third shaft and a paddle blade, that supplies the developer conveyed by the first or the second conveying member to a developing roller, wherein: at least one of the first and second shafts includes a first portion that faces the hole and a second portion that does not face the hole; and a diameter of the at least one of the first and second shafts in at least a part of the first portion is smaller than a diameter in the second portion.