Formulation of Dual Theory in Terms of Functional Integrations

A formulation of dual-symmetric theory is given in terms of functional integrations. Known formulas of the theory, such as the $N$-particle Veneziano amplitude and both planar and nonplanar one-loop amplitudes, are explicitly given in terms of the new formulation. The new formulation is also shown to be equivalent to the other formulations such as the harmonic-oscillator formulation.