Abstract: Apparatus for surface treatment by cataphoresis of metal parts (5) particularly of motor vehicle bodies, supplied by direct current. A tank (1) whose sides carry anodes (2) is provided where the treatment occurs. An overhead conveyor is provided which brings the bodies (5) to be treated in swingtrays spaced apart by a regular spacing .lambda.. A carriage or main body (4) equipped with two contact slides (41, 42) mounted on two parallel conductive rails (11, 12) and located above the tank (1), provide electrical connection to each body. The bodies (5) to be treated effectively becoming the cathodes. The two rails (11, 12) are divided regularly into portions or dividing rails (111, 121) by an insulating material, each portion connected to the negative terminals (31) of rectifiers (3), supplying the current. Each mobile body (4) is always in electrical contact with a divided rail (111, 121) to ensure that no unnecessary cut offs of current occur, thereby preventing coating defects.