PURPOSE: To facilitate adjustment for recognizing a load cradle number in a conveying device along a defined course by storing an identification number on the side of a load cradle and installing an ID card having an optical transmitting/receiving means while providing a reading device on the course side.

CONSTITUTION: An ID card 21 having optical transmitting/receiving elements and a liquid crystal indicator is provided on a transmitting window 22 on the side between rollers 8 of a load cradle 1 and the identification number of its own is stored. A reading device 24 is provided in a position opposite to the ID card 21, along a traveling course composed of a machine frame 2. The reading device 24 has optical transferring/receiving elements on the transmitting window and is connected to a control device. In this structure, the reading device 24 transmits a load-cradle's own number transmitting command in accordance with the traveling speed of the load cradle 1. The load cradle 1 transmits its own number to the reading device 24 in accordance with this command and the reading device 24 recognizes the load cradle number. Thereby, adjustment can be facilitated.