Our aim is to devise a method that measures distributed load, such as surface pressure fluctuation on a structure. This paper conveys its possibilities and limitations by attempting to estimate the distributed load on a simple beam. An indirect method that can measure the distributed load of a vibration system, which can be a beam or plate, is proposed. This method essentially transforms the differential equation that governs the structure to "instrument domain". The instrument domain defines the coordinates of which we can measure the physical variable of interest, with the smallest error as possible as one can. The excitation laod on a beam is evaluated by measuring the outputs of vibration system e.g. strain, acceleration. In this paper, basic theory of the proposed method and the experimental results that validate the method are presented.