It is assumed that the interaction between elementary particles is characterized by an effective range which dependence only on the mass of particles transferring the interaction. It is demonstrated that if all masses and together with them the interaction range are fixed, unitarity and analycity lead to restriction of possible value of πN-coupling constant and also of the absolute value of the ππ-scattering amplitude at zero energy (if it is negative). The proof is carried out by employing the dispersion relations for the inverse function of the forward scattering amplitude.