We have developed a differential pressure measurement technique using pressure-sensitive paints to measure small pressure fluctuations with high accuracy. The application of PSP to the measurement of small pressure fluctuations has been widely studied. However, the change in luminescent intensity due to pressure variation of 100 Pa near atmospheric pressure is less than 0.1%. Furthermore, the resolution of a 12-bit (4096 gradations) high-speed camera is insufficient to measure such small fluctuations, which hinders the improvement of measurement accuracy. This study proposes a PSP technique to measure small pressure fluctuations with high resolution using a photomultiplier tube (PMT) that outputs an analog signal. The analog output signal of the PMT was filtered to separate the AC and DC components, and the small AC component was measured with high resolution to improve the accuracy. We conducted a verification test using a resonance tube to measure small pressure p fluctuations and succeeded in measuring the pressure fluctuation of Pp-p ~ 47 Pa at 155 Hz with high S/N. We also tried to apply this technique to measuring two-dimensional pressure fluctuation fields using a resonance cavity. We have demonstrated that a two-dimensional p pressure fluctuation field of Pp-p ~ 50 Pa at 1300 Hz can be measured without any special post-signal processing for noise reduction.