In a water flow detection device in which signals are output in response to movement of a detection rod that rotates in conjunction with the opening of a valve body, a pin that supports the detection rod is capable of being provided so as to be constantly parallel to a valve shaft of the valve body, and a water flow is capable of being accurately detected by the rotation of the detection rod while the detection rod contacts the valve body without being inclined, the detection rod rotating in response to opening and closing of the valve body. Accordingly, the water flow detection device includes a retainer and an extended block as holding members that hold the pin of the detection rod such that the pin is parallel to the valve shaft of the valve body, the retainer having a bearing for the pin, and the extended block holding the retainer to fix the retainer to the main body with a bolt. Furthermore, the retainer and the extended block respectively have a protrusion and a groove as rotation-restricting sections, and these members engage with each other.