  The paper deals with a boundary value problem for the nonlinear
integro-differential equation $u^{\prime\prime\prime\prime}-m\left(\int_0^l
{u^\prime}^2dx\right)u^{\prime\prime}=f(x,u,u^\prime), \; m(z)\geq \alpha>0, \;
0\leq z <\infty$, modelling the static state of the Kirchhoff beam. The problem
is reduced to a nonlinear integral equation which is solved using the Picard
iteration method. The convergence of the iteration process is established and
the error estimate is obtained.
