To provide an air compressing device stably generating high-pressure compressed air from a low-pressure air compressor without using a high-pressure air compressor.

The compressed air from an air compressor 40 is guided through a compressed air tank 10A and a booster valve 61, and high-pressure compressed air having no pulsation is generated in a high-pressure air tank 10B. Dehydration and dust removal are applied to the compressed air between the compressed air tank 10A and the booster valve 61 so that the booster valve 61 and a pneumatic apparatus section 50 are smoothly operated. When the high-pressure compressed air stored in the high-pressure air tank 10B is used for the pneumatic apparatus section 50, the air from the high-pressure air tank 10B can be easily cut off in a single operation.