A waste toner collecting device includes: a waste toner collecting bag being stretchable; a toner conveyance part fitted with the waste toner collecting bag, and conveying a waste toner and also discharging the waste toner toward the waste toner collecting bag; and a holding member for the waste toner collecting bag, which holding member is attached to a terminal end part of the waste toner collecting bag, is capable of being fitted to the toner conveyance part by holding the waste toner collecting bag between the holding member and the toner conveyance part while folding the waste toner collecting bag more compactly than in a used state, and is attachable to and removable from the toner conveyance part.