This is a minute differential pressure gauge with high reliability, equipped with magnetic couplings as the expanding mechanism. This pressure gauge is used to detect the pressure difference due to pressure loss in air filters of air conditioners for checking and controlling the clogged conditions of air filters. This pressure gauge can also be applied for checking and controlling interior pressure of clean and bioclean rooms. Additionally, this pressure gauge can be used as a micropressure gauge by opening its low pressure side to the atmosphere.