An electrostatic copying apparatus comprising a lower supporting frame, an upper supporting frame mounted on the lower supporting frame for pivotal movement between an open position and a closed position, a document placing means having a transparent plate for placing a document to be copied thereon, an optical unit and a driving source. Either the document placing means or at least a part of the optical unit is mounted reciprocally on the upper supporting frame and drivingly coupled to the driving source via a power transmission mechanism. The apparatus further includes an automatic locking means for automatically locking the document placing means or at least a part of the optical unit and cancelling the locking according to an operation of moving the upper supporting frame to an open or closed position or an operation incident to this moving operation.