To obtain a control method of a workpiece carrying device, which employs an optical communication system having resistance to noise, has high reliability for the position displacement of a carriage, and is inexpensively constituted.

The control device is composed of: proximity switches 37, 38, 39 and a position detecting plate 40 which detect the carriage 7 in the specified position of a guide rail 6; a controller 31 provided on a fixed side; an encoder for detecting a current position of the carriage 7; and a communication means for giving and receiving the data by the optical communication between the encoder and the controller 31. The controller 31 has a storage device for storing the position data for the specified position of the carriage 7, compares the position data stored in the storage device with the current position data of the carriage 7 transmitted from the encoder through the communication means, and determines whether the difference is within an allowance.