Abstract: A respirator (1) is composed of a respirator casing having a pair of rectangularly contoured frames (12) mounted around rectangular apertures (11) on respective sides of the respirator (1). The apertures (11) are adapted to receive a pair of air filter sets to filter out foreign particles and provide clean air to the wearer. Each filter set (2) is composed of inner and outer filters (21 and 22). Each of the inner and outer filters (21 and 22) includes a receiving frame (213 and 223) adapted to receive a dust protective layer (214 and 224) by means of a respective cover (215 and 225) to press the respective dust protective layer (214 and 224) inwardly. Upon the air filter set (2) being mounted in the frame (12) of the respirator (1), an air passage is formed between the inner and outer filters (21 and 22) for air to flow and most of the dirty particles are blocked from passage and are entrapped on the dust protective layer (214 and 224) to allow clean air to pass into the respirator (1).