A cleaning unit is equipped with a cleaning blade that is in contact with a surface of a photosensitive drum and cleans the surface. A peak temperature of a loss tangent (tan .delta.) is in a range of 2.degree. C. to -30.degree. C. when a sine-wave vibration of 10 Hz is applied to the cleaning blade. Moreover, the cleaning unit lowers a coefficient of static friction of the surface of the photosensitive drum that is to be cleaned.