A method for sound field reproduction with the suppression of exterior radiation is proposed, which makes it possible to synthesize a desired sound field in a reverberant environment without prior knowledge of the transfer functions of the multiple loudspeakers. The objective function used to achieve this is formulated as the weighted sum of the interior reproduction error and exterior radiation power. The optimal driving signals are derived by harmonic expansion of both the interior and exterior sound fields. In contrast to the empirical coefficient truncation in the state of the art, in the proposed method, an optimal weighting of the harmonic coefficients is derived analytically. Numerical simulation results indicated that high interior reproduction accuracy and exterior power suppression can be achieved by the proposed method compared with the mode-matching method using harmonic-order truncation owing to the optimal weighting.