Although the meson mass spectrum calculated from the simple harmonic potential by the B-S equation fits the experimental data fairly well, the wave function so obtained leads however to unreasonable results when applied to calculate the electromagnetic form factor, which turns out to be complex for space-like q2. It is argued that the reason for this lies in the fact that such a wave function does not possess the correct analytical property for the variable p0. In order to guarantee this analyti-city as well as to maintain the covariant form, it is adequate to express the wave function in the form of an integral representation according to a theorem proved by Dyson. Furthermore, some summation rules for the spectral function in the integral representation are derived with the physical condition that the wave function should be finite at x = 0.