In this paper, we present a novel framework of beamforming robust for a microphone array rotation. In most array signal processing methods, the time-invariant transfer system from a source to a microphone is assumed for calculating a spatial filter. This assumption makes it difficult to use the microphone array in real situations since sources and the microphone array may move. In this work, we focus on one such movement, the array’s rotation. The key in our method is to use a regularly circular microphone array where microphones are equally spaced on a circle’s circumference. Based on this, we propose a method to interpolate the sound field on the circumference. The interpolation enables us to estimate the signals at the microphone positions before the rotation even when the array rotates. Hence, the conventional array signal processing assuming the time-invariant system is applicable. Simulation results indicated that the proposed method improves the beamformer’s performance under the array rotation.