A wireless transmission device for use in a robot arm is disclosed to include a rotating unit including a first winding and a second winding relatively rotatably arranged in a coaxial manner, and two receiver-transmitter units respectively electrically connected to the first winding and the first winding for receiving a composite signal and then generating a power signal and a control signal. Thus, the receiver-transmitter units can transmit power and data in two ways by means of an electromagnetic coupling between the first winding and the second winding, having the advantages of simple structure and no need for wiring, and allowing the robot arm using the wireless transmission device to be freely rotated through 360 degrees.