To provide a wattmeter box mounting method that is mountable horizontally on a wall surface without the use of a particular apparatus or modification into a particular structure.

The wattmeter box is characterized in that reference graduation 7 is indicated at the bottom part of a base board 2, the wattmeter box 1 is mounted horizontally and vertically, by hooking a piece of string 9 with a weight 8 on a mounting screw 5 for mounting the wattmeter box 1 on the wall surface, and by matching the reference graduation 7 with the string 9 having the weight 8.