The present disclosure provides a drive transmission apparatus including a swing gear mechanism and capable of reducing the workload during assembly and improving efficiency of the assembly operation. A first swing gear, which transmits rotation of a first input gear that is driven by a driving force, is held by a first swing member. The first swing member includes a first engagement portion engaging with a supporting portion, and swings around an axis of the first input gear. The first engagement portion is formed so as to be attached to and detached from the supporting portion if the first swing member is moved in a radial direction with respect to the axis.