To reduce noise, facilitate an assembling operation and a disassembling operation for repair by reducing the number of fixed points of a cover, and reduce weight.

This portable air compressor comprises a compressor body 5 having a motor 4 at one end of a crankcase 3 with a compressor, an air tank 6 disposed on the compressor body, and the cover 7 for covering the compressor body. A mounting piece 61 projects from the cover in one of the longitudinal and lateral directions. A cover mounting groove 58 corresponding to the mounting piece 61 is formed in at least one of the compressor body and the air tank. The mounting piece 61 is inserted into the mounting groove 58 through a first buffer 62. The cover 7 is screwed to a cover mounting part formed on at least the other of the compressor body and the air tank through a buffer 63.