Many diversion apparatus from open canal are set in many agricultual area and projects. The investigations on the improvements of the accuracy and the hydraulic functions of the automatic diversion control devices are, so far, not enough. Generally pipes in the bank, orifices and sluice gates in diversion works have been used for water diversion from open canal. These traditional diversion apparatus have originally the peculiar defects that the diversion discharge is affected due to the variaion of water level of the canal. To prevent this variation, engineers have used the check gates in the canal, but these gates sometimes artificially disturb water flow in the canal. The automatic diversion apparatus is demanded to have a simple structure and high accuracy from the standpoints of saving the water and labour in the management of water uses. With some experimental results, this paper deals with the hydraulics of the apparatus with stop plate, its simulation model of the diversion work and its application to the Neribeya diversion works in Toban Irrigation Project.