An improved technique has been suggested for identifying multiple input forces acting on a structure by using multiple vibration measurements and a stored frequency response function matrix. By applying the regularization method based on singular value decomposition in the frequency domain, it is shown that uncertainties on the force estimation which are mainly caused by potential singularities of noise contaminated transfer function matrix, can be eliminated effectively. Optimization criterion for the iterative selection of regularization constant is suggested to minimize the noise content of the estimated forces as long as maintaining its accuracy. Illustrative simulation and experiments are presented to verify the criterion as well as to show that the technique is effective for multiple force identifications.