The interaction between a linear polymer and an interface is studied for three types of surfaces: reflective, attractive, and repulsive. The freely jointed chain model is assumed in the equation of diffusion approach, with volume exclusion effects neglected. In this case, the distribution function of the polymer is derived with the assumption that one or both ends of the polymer are bound to the interface. We evaluate the mean thickness of the polymer layer, the average number of adsorbed monomers, and the mean distance of the monomers from the surface. When one end of the polymer is bound to the interface, the results are qualitatively compatible with those of the previous lattice models. When both ends are bound, the polymer stays nearer to the interface but the macroscopic mean values stay qualitatively the same.