A physiological signal processing device is provided. The physiological signal processing device includes a patch, a plurality of electrodes and a processing device. The plurality of electrodes detect an Electrocardiography (ECG) signal. The processing device is configured in the patch and is coupled to the plurality of electrodes to receive the ECG signal. Furthermore, according to the ECG signal, the processing device calculates a first differential value between a voltage of an R wave of the ECG signal and a reference ECG value, and determines whether the first differential value is greater than or equal to a first threshold to determine whether to adjust the positions of the electrodes. When the positions of the electrodes are determined, the processing device obtains heartbeat information and/or breathing information according to the ECG signal.