To provide an in-line coating device, an in-line coating method, and a separator which provide high mass production and are capable of applying appropriate bias voltage to workpieces. An in-line-coating device 10 includes: a coating section 12 configured to perform coating of a workpiece W and provided with aligned coating materials 121 to 124; a transport section 13 configured to transport a plurality of the workpieces such that the workpieces face coating materials in the coating section; and a voltage applying section 14 configured to apply, to the workpiece, a bias voltage to attract particles emitted from the coating materials toward the workpiece. The voltage applying section is configured such that the bias voltage applied by the voltage applying section when the workpiece faces one of the coating materials can be different from the bias voltage applied by the voltage applying section when the workpiece faces another one of the coating materials.