A drive-side coupling part of a drive transmission mechanism includes: a base including a first opposed surface facing a driven-side coupling part of the drive transmission mechanism in an attached state; a semispherical projection from the first opposed surface at a rotational center of the drive-side coupling part; and a cylindrical projection including an arcuate first projection centered on the rotational center, an arcuate second projection having a shorter inside diameter than the first projection, and a stepped portion between the first and second projections. The driven-side coupling part includes: a base including a second opposed surface facing the drive-side coupling part in the attached state; a columnar projection from the second opposed surface at a rotational center of the driven-side coupling part; a radially-extended peripheral projection on a periphery of the columnar projection; and a recess depressed from a top surface of the columnar projection at the rotational center.