An electrostatic copying apparatus equipped with a first and second supporting frames connected to each other for relative pivotal movement between an open position and a closed position. The first supporting frame has provided therein a rotatably mounted interlocking input gear and a first power transmission system drivingly connected to the interlocking input gear. The second supporting frame has provided therein a drive source, a second power transmission system drivingly connected to the drive source and a rotatably mounted interlocking output gear drivingly connected to the drive source. A pivot member mounted pivotally about the axis of rotation of the interlocking input gear or the interlocking output gear and elastically held at a predetermined angular position by a spring means is provided in the first or second supporting frame. An interlocking linking gear is rotatably mounted on the pivot member. The interlocking linking gear is drivingly connected to the interlocking input gear or the interlocking output gear rotatable over a slight angular range. When the first and second supporting frames are relatively pivoted and brought to the closed position, the interlocking linking gear comes into engagement with the interlocking output or input gear.