To prevent an increase in the number of parts to facilitate assembling.

An electronic unit 3 is put in a case 12 from an opening part 12h as shown by an arrow A and a pin 12e is inserted in the hole 13b of a substrate 13a to set the position of the case 12. A cover 15 is moved in the direction shown by an arrow B to cover the case 12 and the opening part 12h. A dial plate 16 is moved in the direction shown by an arrow C along the front 15b of the cover 15 to be assembled to the front of the cover 15. Locking parts 15g, 15h, 15i prevent the detachment of the dial plate 16. The display of a water use amount on a liquid crystal display device 3 is visually confirmed through a seeing-through part 16a. A locking part not shown in a drawing for preventing the contraction of the interval W between both side walls 12b, 12c of the case is formed to the rear surface of the front wall 15b of the cover 15.