We present a method for performing microwave (MW)-to-optical transduction based on atomic beam magnetic resonance spectroscopy, where laser-induced beam fluorescence bridges two electromagnetic waves with significantly different frequencies. We experimentally demonstrate the real-time demodulation of an infrasonic wave signal encoded in a MW carrier by driving Cs beam Rabi (Ramsey) transition with a single (two separated) MW magnetic field(s), thus validating this method. A high signal-to-noise ratio (SNR) of above 90 dB was achieved for near-full modulation, and a MW field variation as small as 0.02% was detectable with a SNR > 10 dB by utilizing either of the transduction configurations. Our sensitive and continuous atomic beam MW transducers offer a promising platform for atomic communication and MW sensing