To avoid removing work of causing a danger when a controller actually enters the water in a waterway, for removing and releasing a stop-log, when the water in the waterway increases.

This stop-log structure has a column 6A having a projection member 6B having the lower side of a circular arc shape in a lower part and a spring 6C for pressing the projection member 6B to the lower side under predetermined pressure, for realizing the automatic opening function such as automatically opening the stop-log 3, when a water level in the waterway reaches a predetermined water level, and a recessed part member 5A arranged on the bottom wall side of the waterway on the lower side of the column 6A and having an inclined surface 5B for storing and locking the projection member 6B in an ordinary state and gradually becoming high in the downward direction, and also has an adjusting mechanism of adjusting the hooking height of the projection member 6B to the recessed part member 5A in the vertical direction.