A collection vessel 124 has intermediate transfer body collection ports 134 and developing machine collection ports 136. Collected developer occurrence sections placed in intermediate transfer bodies and developing machines are connected to the collection ports 134 and 136. At least two of the collection ports 134 and 136 are formed so that they are arranged in a vertical direction. Collection spaces 148a to 148f to which the collection ports 134 and 136 are connected are separated by partition walls 146, and the collection capacities of the collection spaces 148a to 148f are set according to the heights and shapes of the partition walls 146.