Pressure-Sensitive Paint (PSP) is applied to various wind tunnel tests as a useful technique to measure pressure distribution on model surfaces. PSP is inherently an absolute pressure sensor so that it is difficult to use this technique in low-speed flow where pressure change on a model is very small. To measure pressure with a high degree of accuracy at low speeds, we have developed a new type of PSP that responds to differential pressure rather than absolute pressure. This novel technique uses porous membrane through which gas containing no oxygen (e.g. nitrogen) is transported from the backside to the front side by pressure difference between the two. The transported gas purges oxygen near the surface and luminescence of PSP is enhanced. The results of sample tests show that the pressure sensitivity of the new PSP is higher than that of the current PSP by a factor of 100 times or more. In addition, the response of this sensor to differential pressure is almost linear and highly reproducible.