Myoken Weir is located at the middle reach of the Shinano River in Niigata prefecture. This weir has a fishway in point of view of fish inhabitation. The fishway seems to has good function by judging from the result of the number of salmon caught at the upper fishing ground. This study aims to grasp quantitatively the function of fishway of Myoken Weir and the characteristics of fish behaviors around the fishway.