A drive transmitter for an image forming apparatus comprising: a first coupler mounted on an axial end of a first rotary shaft and provided with extensions, which extend in an axial direction thereof and are arranged at intervals in a rotation direction thereof; a second coupler mounted on an axial end of a second rotary shaft and provided with contact parts to which the respective extensions contact between the first rotary shaft and the second rotary shaft upon drive transmission; and reinforcing ribs provided to the respective extensions and reinforcing the respective extensions; wherein: at least one of the first coupler and the second coupler is mounted on a corresponding one of the first rotary shaft and the second rotary shaft swingably by a given angle with respect to the axial direction; the reinforcing ribs extend from the respective extensions toward a center of rotation of the first coupler and are coupled at the center of rotation; the second coupler includes a rib insertion hole toward the center of rotation to which the reinforcing ribs are inserted, and extension insertion holes to which the extensions are inserted and link to the rib insertion holes; and (D1-D4)/2 > Xsin(θ) is satisfied, where θ represents a maximum inclination angle taken by either one of the first coupler and the second coupler inclinable with respect to the axial direction when the first coupler and the second coupler are coupled, X represents the length of each of the extensions in the axial direction, D1 represents the diameter of a drive coupling circle that links respective centers of the extensions, and D4 represents the inner diameter of the rib insertion hole. a first coupler mounted on an axial end of a first rotary shaft and provided with extensions, which extend in an axial direction thereof and are arranged at intervals in a rotation direction thereof; a second coupler mounted on an axial end of a second rotary shaft and provided with contact parts to which the respective extensions contact between the first rotary shaft and the second rotary shaft upon drive transmission; and reinforcing ribs provided to the respective extensions and reinforcing the respective extensions; wherein: at least one of the first coupler and the second coupler is mounted on a corresponding one of the first rotary shaft and the second rotary shaft swingably by a given angle with respect to the axial direction; the reinforcing ribs extend from the respective extensions toward a center of rotation of the first coupler and are coupled at the center of rotation; the second coupler includes a rib insertion hole toward the center of rotation to which the reinforcing ribs are inserted, and extension insertion holes to which the extensions are inserted and link to the rib insertion holes; and (D1-D4)/2 > Xsin(θ) is satisfied, where θ represents a maximum inclination angle taken by either one of the first coupler and the second coupler inclinable with respect to the axial direction when the first coupler and the second coupler are coupled, X represents the length of each of the extensions in the axial direction, D1 represents the diameter of a drive coupling circle that links respective centers of the extensions, and D4 represents the inner diameter of the rib insertion hole. at least one of the first coupler and the second coupler is mounted on a corresponding one of the first rotary shaft and the second rotary shaft swingably by a given angle with respect to the axial direction; the reinforcing ribs extend from the respective extensions toward a center of rotation of the first coupler and are coupled at the center of rotation; the second coupler includes a rib insertion hole toward the center of rotation to which the reinforcing ribs are inserted, and extension insertion holes to which the extensions are inserted and link to the rib insertion holes; and (D1-D4)/2 > Xsin(θ) is satisfied, where θ represents a maximum inclination angle taken by either one of the first coupler and the second coupler inclinable with respect to the axial direction when the first coupler and the second coupler are coupled, X represents the length of each of the extensions in the axial direction, D1 represents the diameter of a drive coupling circle that links respective centers of the extensions, and D4 represents the inner diameter of the rib insertion hole.