A sheet transport apparatus includes a transport roller for transporting a sheet to the processing section, a driving motor for driving the transport roller, and a driving transmission mechanism. The driving transmission mechanism includes a rotary shaft, a transmission rotary member having a circular fit hole, a holder member with a press-fit hole having a curved part and a flat part, and a coupling mechanism for coupling the holder member and the transmission rotary member. The rotary shaft includes a fitting part having a circular cross section at one end side to be fitted into the circular fit hole, and a press-fit part having a curved part and a flat part press-fitted with the press-fit hole. The coupling mechanism includes a convex portion formed on a side of the transmission rotary member, and a concave portion formed on a side of the holder member press-fitted with the convex portion.