Using the unitarity of the S-matrix, Aizu and Watson have shown some relations between the photomeson production and the meson-nucleon scattering. Their theory is reformulated and generalized here in a summarized form, in order to make facile the analysis of experimental results. Experiments on the photomeson production near threshold energy lead us to suggest some limits on the magnitude of s-phase shifts of the meson-nucleon scattering and on the contribution of the nucleon current.