Image forming apparatus including rotary member speed detection mechanism

An image forming apparatus including a rotary member having an image formation area, and a scale located at a position outside of the image formation area and on an inner circumference of the rotary member. Also included is a drive device configured to drive the rotary member, a developing device configured to develop an image on the image formation area of the rotary member, and a transfer device configured to transfer the image on the image formation area to a recording sheet. Further included is a sensor configured to detect the scale on the rotary member and to output a signal corresponding to the detection of the scale.