[en] The Kyoto University Critical Assembly (KUCA) is a unique critical assembly with three cores; two solid-moderator, one water-moderator heterogeneous cores with highly enriched uranium. In order to keep the safety and to operate this critical assembly smoothly and effectively, a man-machine communication system between the operator and facility has been designed in detail from the various points of view. The control desk and graphical pannel were made so that an operator in the control room can operate the reactor and its attachments in the reactor room and can know their conditions exactly. The following items were considered their sizes, shapes and the mutual arrangements in the control room, furthermore the ways of the display and annunciator, and their arrangements in the pannel. For example, the alarm annunciators are classified both in color and sound so that the tension of an operator increases gradually according to the degree of emergency. Since the first critical experiment, the control desk and graphical pannel have been successfully used to transmit the information precisely to many operators including the researchers from other universities, and have contributed to operate the reactor safely and smoothly. In the present report, the outline of structure of the system and the practical experience are described. (author)