This paper deals with the numerical realisation of the wave-source identification of wavemaker by measuring the radiated waves caused by the wavemaker. The problem is governed by the Fredholm type of integral equation of the first kind, resulting in numerical instability of solution. In order to overcome the difficulty of numerical instability, Landweber regularisation method (stable numerical algorithm) is introduced in this paper. The result of the present study can be applied to the radiation problem for an oscillating ship.