This paper describes the development of a three-component force/moment sensor with plate-beams which may be used for measuring the forces Fx, Fy and the moment Mz simultaneously in industry. In order to make the three-component force/moment sensor, the following procedures are performed. (1) Derivation of equations to predict the bending strains on the surfaces of the plate-beams under the forces or the moments. (2) Determination of the sizes of the sensing elements of the force/moment sensor using the derived equations. (3) Finite Element Method (FEM) analysis for confirming the strains from the theory. (4) Selection of the attachment locations of the strain gauges of each sensor. (5) Fabrication of the three-component force/moment sensor. (6) Characteristic test of the three-component force/moment sensor. The rated strains calculated from the derived equations agree well with the results from the FEM analysis and the experiments. The interference errors of each sensor are less than 1.7%.